: A -> A-
This Pokemon doesn't easily fit on teams, but it deserves more credit than shrang gives it. Rayquaza's defensive niches are related to being anti-Salac Don, anti-Swift Swim, and anti-Deo-A. Mixed set is probably the best, but shrang is right in that the damage output isn't what newer gen Ubers players might expect from something with 150 / 150 offenses. If played correctly you can usually pseudo trade with something, which is a potential boon for offensive teams. CB set isn't too bad either, and those DEs actually lay a ton of damage to defensive Kyogre and Groudon. Putting this down in B is way too harsh, as is the comparison to ORAS Palkia, but it certainly doesn't belong in A rank with the likes of Ho-Oh.
I disagree with this Pokemon moving up. Spin blockers aren't even necessary for Deo-S / Deo-D teams, let alone your common defensive squad. Almost all spinners are Forry, which you can keep in line by just running Fire coverage in the appropriate places. Usually the only other spinner you'll see is Kabu, which Gengar doesn't want to switch into under rain. Main reasons you use this is for the Normal and Ground immunities, but the combination of status, Explosion, and special attacks is also decently effective at stallbreaking in Ubers. You can adapt its moveset to nail all the threats your team wants gone, but like mixed Rayquaza it lacks immediate power and can feel awkward with its moveset.
: B -> B-
Fits on next to no teams and is more of a nuisance than an actual defensive threat. It's outclassed as a Swift Swimmer so you end up running a defensive set with Rain Dish that can't do anything if it gets badly poisoned. Might fall victim to never being developed well rather than having innate flaws, but until then it should probably be ranked lower.
: B -> A-
Ranked far too low for a Steel-type of it's effectiveness. The Ground typing is a huge draw and allows it to fit very well on offensive rain teams. It's also a solid check to a few CB Pokemon like Snorlax and Lugia, and a secondary or tertiary Lati check. Several common CB mon checks (think Rock- and Steel-types) are scared of EQ while you can potentially trade via boom against defensive Kyogre or Groudon, two Pokemon most rain offenses want gone. It's simply better than the Steel-types in B+.
Like mixed Rayquaza and Gengar it's not immediately obvious what the offensive and defensive draws are. The set I like the most is mixed, which allows you to bait out and punish a variety of threats since ttar's offensive stats aren't bad and it has an expansive movepool. Sets like T Wave + Rock Slide can also be annoying so long as you have the necessary support. It's defensive traits aren't extensive, but it is sort of a Rayquaza, Ho-Oh, Lugia, and Lati check, while sand neutralizes Leftovers, Thunder, and weather sweepers.
: B- -> B
This should probably be ranked in the same class as Deo-D. You're a bit worse at tanking stuff when it comes to laying Spikes, but the Speed and increased power can be annoying to opposing teams since you can run things like Knock Off, Ice Beam, and Fire Punch. Also can work as an emergency Salac Don check.
: B- -> C
Never seen this Pokemon do anything worthwhile or justify its spot on a team. Any non-gimmick set it has is largely outclassed by Mewtwo. Again it might be due to a lack of being developed, but until then it should be dropped.
: C -> B
Actually a legit Pokemon. It Wish passes effectively, especially to Steel-types, and switches into most CB Pokemon well thanks to Intimidate. Toxic + Fire Blast allows you to lay damage against most of the Pokemon you want to check and the additional Ground immunity can also be handy. A good support Pokemon for certain defensive teams.
: C -> B
Also sort of legit. Best set is max Speed with Double-Edge. Being faster than 252 Lati and everything below for a CB user of this power is very appealing, and unlike Deo-A it can actually take a hit and offers some superficial defensive synergy via a Ghost immunity. Shrang is right in that the forced switch turn isn't a huge problem as a single turn isn't as deadly when compared to newer gens, but it is something that builds still need to account for. Works fine in a lead position, but keeping it hidden can also be an advantage.
: Unranked -> C
Virtually always inferior to Snorlax or Slaking. I don't get how you justify this Pokemon when its only advantages over its competitors are 10 more base Speed (which doesn't really help since you still don't beat max Lati) and Intimidate (which doesn't help since you are fragile and don't want to switch into CB mons).
: Unranked -> B
Faster than Lati CB user, sort of a Ho-Oh check, and emergency check to Salac Don. Works best as a cleaner on a Spikes offense, although its use makes it harder to fit a Steel-type. Seems on par with the Deo Spikers, ttar, and Eggy.
: Unranked -> B-
Gives a way to slightly deviate from a standard sun stall or balance arrangement. Unfortunately it's worse off against Groudon and defensive Kyogre than several other CB users and still doesn't really want to switch into Ho-Oh.
: Unranked -> C
An interesting defensive cleric since it frees up Blissey. I've seen other people use different sets as well. Not convinced it's worthwhile to use, but putting it in C rank will let people know it's around.