Just got reqs. Here are some of my thoughts fresh off of laddering.
1. My stance on Tera is no longer Tera Preview + other options, or single Tera. Tera Ban is the most healthy option by far. While I very much appreciate the defensive utility Tera provides to mons like Dondozo, Skeledirge, and Ting-Lu, the amount of unpredictability is very difficult to deal with on offensive threats. Tera encourages much more passive gameplay, as you have to scout out every potential tera option. I'd find myself tending to just hit u-turn/volt switch everytime I'd approach something like a Roaring Moon rather than immediately attack it, just in case it would tera into something completely unexpected (quite a few tera fire roaring moon and tera dark brelooms on ladder). Its already hard to slot defensive options that cover the entire metagame without running balance/stall, but slotting these defensive options trying to cover potential tera types is incredibly difficult. Most of the time I'd end up trying to out offense a team before they could tera and catch me off guard, or just Chi-Yu nuking their tera option.
2. As soon as Tera goes, Chi-Yu has to go. Tera is the only realistic counterplay to Chi-Yu, bar mons like AV Azumarill and Quaquaval (both of which can't switch into Chi-Yu with tera and don't like taking hits regardless). Under sun, Specs Chi-Yu is impossible to switch into. Its not a slow mon by any means and the only real way of beating it is by sacking a mon to revenge it, or just hard switching one of the few checks to it like Roaring Moon(which needs SpDef investment to live a sun boosted Specs Chi-Yu). Chi-Yu is singlehandedly the most problematic mon outside of Tera and truly has no counterplay outside of garbage sets like AV Azumarill (walled by Torkoal and Scream Tail on most sun teams). A lot of the time games would come down to you and your opponent sacking something to your respective Chi-Yus and hoping you win a speed tie at the final Chi-Yu v Chi-Yu showdown. It really feels like a supercharged Tapu Lele.
3. Gholdengo is even more oppressive than I initially thought. The most common forms of removal are Great Tusk, Iron Treads, and Corviknight. These all cannot switch into Gholdengo, and Balloon renders Tusk incredibly useless. In most games, hazards stayed up the whole time regardless of what else went on. Gholdengo is just making an already incredibly offensive metagame more offensive. Granted, this is nowhere near as much of a problem as Chi-Yu or Terastallization so I wouldn't mind seeing this stay for some time. Speaking of removal though, Hatterene feels incredible, and puts in work with calm mind/nuzzle/draining kiss every single game, especially since Hatterene is one of the few ways to keep hazards off. It can't switch into Glimmora or Gholdengo though, but it pressures setters such as Tusk and Ting-Lu. Talonflame also feels alright thanks to its Gholdengo matchup, but is deadweight against Glimmora, and wants to run U-turn over Defog a lot of the time.
4. If I were to rate specific team structures, I would definitely rank it as Sun > Gholdengo Hazard Stack BO > Grimmsnarl/Cyclizar HO > Balance > Bulky Offense > Stall. That's not to say that Stall is necessarily awful, but it very much struggles with the most prominent wallbreakers, Chien Pao and Chi-Yu, and cannot hold up against Sun at all. In fact, Sun singlehandedly feels like it can beat any other playstyle, thanks to having Tusk + Roaring Moon + Chi-Yu along with their respective teras. Sun also has other great options like Sandy Shocks, Scream Tail, Gholdengo, Glimmora, Hatterene, Dragapult, Dragonite, etc. You can really slot any two mons after Tusk, RM, Chi-Yu, and Torkoal to make certain matchups better. It feels significantly better than any other playstyle and really abuses the most broken aspects of the tier to the fullest.
While I did feel like there was a skill level required to predict correctly with tera + keep momentum in a game, each match felt like a coinflip until both players use their tera. Every single play made seemed like it had to be a midground or you'd be punished for not expecting a specific tera. I actually had the most success running an offensive team with a ton of wallbreakers rather than setup sweepers, because that would let me dish out incredibly strong midground plays regardless of Tera. But with teams that were more defensive, it was a lot harder to switch around and make midground plays, since hazards would always take a toll on my core regardless of what I did.
Ultimately though, I think the OU council has done well with everything thats happened, and I think that the tier has a lot of potential, but Terastallization (and Chi-Yu) are too much for the tier.