Alot of mons in the tier run Ground or Fighting coverage, which can make it difficult to splash Tran on teams. I’ve found success with Balloon Tran which lets it hardwall non-Dragon STAB Gfire and check Volc slightly better. You could also opt for Flame Body since it punishes the plethora of physical attackers in the tier, especially the T-Axel mashers.
While I wouldn't say the meta isn’t completely balanced. Moon is still busted, Deo-S is too effective at it’s job, and Kyu might end up broken in the future, I have to agree that the new additions help balance out the meta and it makes the SV OU feel fresh again. There are two mons that I’ve come to really love in this metagame that contribute to teambuilding.
Raging Bolt is fucking awesome. A bulky wallbreaker with priority. Having that Electric/Dragon typing with that bulk is just really nice to have for that Water resistance. You have no idea how much role compression that fills. Previously the role of priority was filled by mostly Gambit, Rilla, and Dnite. Electric priority is also incredibly useful to have with all the Tera Flyings in the world. Also it could just end games with a CM sweep outright.
Hydrapple has my favorite design but also has so much to offer in the builder. A bulky Regen pivot with the ability to break holes. Balance teams, especially Boots spam, longed for something like this. As a problem with Boots spam was that it is hard to slot in ways of making progress, since stuff like Band or Specs are off the table. Most Balance structures went with Pult, but it sometimes lacked that raw power in certain matchups. Hydrapple can not only check Boulder, Rilla, and Hamu in one slot, it could break. I’ve also messed around with AV and RH NP. Fantastic mon that will get better after tier shifts.
There is just a ton of off-meta picks that have resurfaced like you said. Keldeo, Primarina, G-Weez, Ttar. Hell I would argue Hippo has a niche in the meta, as it checks Gfire, Boulder, and can Whirlwind away pesky Booster mons. The meta isn’t perfect, but I never wanna go back to the bland broken mess of the previous metas.
is a neat trick room setter due to trick room, teleport, and hazards for role compression. And secondly because 
Ursaluna OHKO-ing stuff with no setup gives me those endorphins I need to keep living.
with grassy seed and suddenly I'm up to the 1800s. Shout outs to Banded Scizor 
who has been a fantastic addition. Catching a Tusk on the switch with a terrain boosted, technician boosted trailblaze doesn't quite give me the same endorphins as Ursaluna, but it's close.
is the only mon I'd vote ban on right now. Volcarona 
has been a problem too, but it feels more matchup-fishy depending on what moves it has. It was funny being able to completely wall one with Latias since tera ground is the most common tera and a lot of them don't run bug buzz. On the flip side, Heatran is just not a counter to it anymore. Can't even toxic it, and some of them even setup in your face. 
, I love having flame body on this thing. Burning everything from Meowscarada, Cinderace, even stuff like Tusk and Lando if you're ballsy enough to switch in on a u-turn or stay in on a rapid spin. What's great is, unlike Moltres, people don't play around you having it, so you get so many cheap-ass burns off doing the unexpected. No fire immunity hardly matters when nobody wants to shoot off a fire move into a Heatran in the first place.
is absolutely not banworthy in the slightest. It's not even the best hazard setter when you have auto-setting Samurott and immortal Ting-Lu and Gliscor. What is neat about it is the variety, since you're never sure if it's screens or scarf trick or life orb or hazards on preview, but that doesn't make it broken.
will solve the issue. There's too many incredible hazard setters and too few removers. The only defoggers worth even considering in OU are Corv and Mandibuzz, both of whom get shut down by taunt on Gliscor or Samurott. It's not like there aren't other great spinblocker options with Dragapult, or even more niche options like Ceruledge or Matcha Gatcha. I guess boots-spam is our only saviour.
