I agree with most of the points you pointed out and it seems the root of the issue is more Zacian than Calyrex to be fair.
i’m not saying the meta did not develop in gen 6, just that at the release of the meta people were toying with new mons, so no creativity at first. This meta is new, DLC has been out for like a month or two!
As to current gen, the fact that Yveltal and NDM are everywhere is not only because they deal well with Zacian and Caly. They check as well: Xerneas, Mewtwo, Calyrex-Ice, Lunala, Solgaleo, Lugia, Giratina-O, Marshadow to an extent if Yveltal has some def invest and Oblivion wing.
Now about Calyrex: if you don’t want to use Yveltal/Mandibuzz, you can use Umbreon which is far from being bad, Porygon 2 with foul play, Ttar with rest and crunch if you want to always have a shot to switch in and don’t forget that it can be paired with driller that beats Zacian! If you really want to be creative, use Incineroar, it wins easily as well. Lastly you have Zarude that can have a little niche in the tier. Why people use Yveletal: because it has an excellent speed tier for a defensive mon, the fact it has access to defog and Dark Aura makes it Knock off and Foul Play hit hard and the access to u-turn can on the switch allow you to send a big hitter. If you want to be cool you can also use Galarian Moltres!
About Zacian: it basically depends on the move it’s running: if it’s SD Behemoth CC Play Rough/Assurance/Wild Charge you basically pick your own counters. Which is true that this mon has no unconditional switch ins bar Quagsire and Necrozma Dusk mane. But if it lacks a dark move, Shedinja walls it. If it lacks an electric move, Ho-oh, Toxapex and even Pyukumuku walls it. If it lacks play rough, it misses out some potential KOs on like Giratina (which sucks). The point is: I agree that this is the most dangerous threat but I don’t see how it’s different from Rayquaza in gen 4, that had little counters depending on the move it picked.
I’m not saying those two are not ok for a suspect. I just don’t think people are trying as much as when gen 8 started to be creative. We used to see Corvi, Skarmory at a point to deal with Zacian, since it would almost autokill itself with recoil and rocky helmet. I have yet to see one sun or sand team in the meta. It will get more diversified once people start testing more and more playstyles. The fact we had the new DLC had a lot of legendaries made it so people are toying with the influx of legendaries the dlc gave, in my opinion. The same way gen 6 started to get creative and found ways to deal with Xerneas and stuff, I’m pretty positive this meta will too, especially when an eventual dlc 3 will come out and bring back Arceus, Meloetta (100% counters Calyrex) and stuff. I’ll for sure continue trying out different stuff because I have been enjoying the meta now to be fair.
I don't even know where to begin with this, so i'm gonna start with from the bottom and work my way up. First off, there's a very good reason why we haven't seen Sand or Sun teams much atall and it revolves on what changed in the meta.
First off, Zygarde invalidates Excadrill offensively fairly easily, and Excadrill was the main reason to pull up with sand in the first place. If Zygarde can swallow a life orb +2 Groudon precipice blades on a roll, its going to swallow an Excadrill earthquake like it just ate some Pepto Bismo prior, smooth sailing from there. Even if you don't have a zygarde, using driller sand is such a matchup fish rn that it's not worth it, with hardly enough worthwhile gains to make it worthwhile. When Sand has so many common enemies like Kyogre, Groudon, Zygarde, and even more "Niche" stuff like Giratina-O, Lugia, and Rayquaza. Sure if you run into a Zacian Caly-G Ho-oh Necrozma-DM Eternatus Yveltal squad you can probably smash it but it's usually not worth bringing unless you KNOW your opp is bringing something that WILL get smashed. The only time i saw Sand smoke someone is when 64 squares pulled up to Nora with a Super CT that makes Roomtours scouters look mild in CPL.
As for Sun, It reasonably
could be explored more, sure, but there's a bunch of other issues with sun you have to deal with. For starters, Slapping a heat rock on a Groudon is a very painful waste of a Groudon. Even beyond this, which is a slight pain compared what else you gonna deal with. First off, the removal of dynamax basically nulled Charizard as an effective Solar power abuser due to its more apparently lack of speed boosting and way to muscle past Eternatus, which we'll get to Etern later.
For Chlorophyll sweepers, aka your primary sun sweepers, have a Litany of issues on their own. Vileplume and Victreebel are turbo Budget Venusaurs, and tbh i'd rather use Ivysaur over Vileplume too. Shiftry is decent, but struggles with 4MSS, you need dark pulse for Calyrex/Necrozma/Zekrom/Dialga/Lugia. You need Grass stab to smack Groudon and Zygardes and punish a Kyogre trying to go hard into you. You need Heat wave for Zacian, want Extrasensory for Eternatus, Rock slide for Ho-oh, and even then you want to be able to boost with Growth or SD. and even if you could fit all of this your wanting for power on your grass stab since if you run solar blade/solar beam, Scarf kyogre can raw into a solar blade and ice beam your Shiftry to the shadow realm. If Explosion never got nerfed i'd give it a nod as an option but it did so yea lol.
Exeggutor sounds absolutely flames i cannot lie, but at the same time it's got problems aswell. While it could run a mixed set w Psychic Ancient Power Grass stab + Stomping tantrum/Sleep powder, it still is forced to run timid/naive to outspeed Calyrex, which also btw, invalidates Vileplume as a decent option. Ideally Sleep power Grass rock psychic would be best, but go tell Mr. 55% usage Dusk Mane to say hi to eggy and you'll see the issue here pretty soon. BTW stomping tantrum will do like 30% max so yea. Your also giving it 75% recovery for free so forget chipping it too.
Tangrowth and Bellosom are too slow and both have no weather ball, Whimsicott has less power than QUAGSIRE, so LOOOOL to that mon, Spikes isn't saving Maractus when it's walled by eternatus with 0 PP on all damaging moves, Lilligant has less Coverage than Regieleki, and then you get to the final pokemon, Leafeon looks ok on paper but then you peep the beautiful Yveltal at usage number bloody 2, and realize you aren't breaking that. Even beyond Yveltal, Eternatus doesn't even die to +2 power herb dig after rocks, and Ho-oh, while not appreciating knock off, will block you at least once.
Solar power is useless since you are never pulling up with Heliolisk, and zard is invalidated. Sun's abusers just have too many problems to be considered worth using an a dedicated play style. If anything, i could see Sun with Banded Ho-oh + DD weather ball kyurem black to snipe Necrozma but other than that i don't see sun working in this meta.
As for the creativity for dealing w Zacian + Caly, literally only eternamax can handle them both in 1 slot, and i covered what handles them up above.
As for the checks you labeled for Caly-G. All i see is a complete deadslot if you don't fight a Calyrex, and even if you do most of these can get Tricked and become more worthless than Current day Mewtwo. Incin only can switch into Necro in the entire tier otherwise and knock it for 40 and never do more again, besides give intimidate support. PLEASE don't tell me Zarude is good because it just isn't. I love my grass type losing to sub glare coil Zygod 1v1, its entirely free Zacian entry. Umbreon is asking to be tricked, Porygon-2 prays in the morning asking to be tricked, Galarian Moltres is absolutely terrible, do not come at me telling me to use a lite version of Mandibuzz, who spoilers; is Fisher Price Yveltal. You can look cool losing the game, hf w that.
And finally, the absolutely NUCLEAR take of Rayquaza in gen 4 being compared to Zacian. I genuinely spit of my pizza pop all over my desk reading this take. You could fuel 10 nuclear reactors with this take.
Anyway, let me talk bout this. 1st off, i explained why Excadrill is mid above, go read that. that's not even the biggest problem here. First off, your criminally underrating Zacian's variety here. Who says it needs SD or even behemoth blade actually. Play rough Close Combat Wild charge Assurance is imo the best set. You don't need Behemoth blade, especially since Xerneas drops to 1 play rough thanks to Fairy Aura. Assurance smashed Necro after rocks and removes Shed as a stopgap, Play rough decks Giratina praying to Hades to not be play rough and to hand it a wisp, and Zygarde is getting stomped. Wild charge invalidates Ho-oh after like 15% chip, and NOBODY will be caught using Pyukumuku anyway. This set alone covers every soft "check" this mon has/had on its own, and if it doesn't have this set it has like 8 other variants it can use. Agility, SD, Rest talk, any pick off 4 attacks, etc. Also on the topic of sun, i could see Solar blade being slapped on for fun to open way for another Physical Sweeper, or even your own Zacian, so that's another thing Zacian can do.
Btw half the mons you listed that are checks by NDM/Yveltal are mid. Caly-ice is mid, Mewtwo is TRASH, Lunala is decent defensively but even then its meh, i have not seen a single Solgaleo in 6 months of playing this tier, do not even give that mon the time of day. Lugia is above average but i rarely see it either, so i can't comment but ik it has a role. These 2 are truly only used the way they are rn because of Zacian and Caly-G, nobody would be caught using snarl yveltal if calyrex didnt exist and do not cap in my presence and say anyone would LMAO. Quagsire would see a pretty net 0.004% usage if zacian did not exist. And necrozma would be able to run literally any other set besides max max impish if it could.
These 2 mons chokeslam any ability to mess around with teams to any level on consistency, look at the guys builder up above to see that in 4k.