endless loop of bans yet still unhealthy. :\ meh
Here's the full set of fresh bans this gen, and how much terastalization factored into it.
Koraidon/Miraidon - zero. Standard cover legendary ban, never had a chance.
* Houndstone - zero. The doggo is banned for Last Respects, and Last Respects only; without that move, it's a physical wall that probably slots nicely into one of the lower tiers. Last Respects is a quickban the moment a second user appears, and Houndstone will be unbanned.
* Flutter Mane - zero. 135 SpA, 135 Speed with three immunities and hitting one of its two weaknesses with a super effective STAB is pretty good, who could have guessed? Didn't last long enough for terastalization to even matter.
* Palafin - zero. Good defensive typing, monstrous stats, three excellent STAB moves (priority, pivoting, 120 BP), he can use terastalization to hit even harder, sure, but doesn't need it and was a sure-thing ban without it.
* Iron Bundle - zero. Unresisted STAB combo off 124 SpA while being the second fastest mon in S/V? Solid physical bulk, while almost all the priority being used is physical? He's busted regardless.
* Chi-Yu - zero. While a fantastic user of terastalization, it doesn't need the boost to be a problem. Specs Chi-Yu in sun has no safe switch ins, being able to reliably 2HKO 252/252+ Blissey with just stealth rock chip. It's an Uber with or without tera in the meta.
* Cyclizar - zero. Fast Regenerator
subpass Shed Tail is why it got banned, and it was problematic with enough recipients that terastalization wasn't the problem on that side, either.
* Annihilape - minor to moderate. Rage Fist and high bulk was already a problem for teams to handle defensively, the ability to swap types just made it worse. It probably wouldn't have been a quick ban otherwise, but I don't think it survives the suspect test. Still, tera was an important part of the ban.
* Chien-Pao - moderate. It was
such a good abuser of tera-Dark that everyone focused on that, but the name Mega-Weavile wasn't just a joke. Like Annihilape, it's probably banned either way, but that's much more speculative because of just how commonly it terastalized.
* Espathra - moderate to major. Getting rid of a poor defensive typing is hugely valuable, but even without tera it has a very limited pool of answers. At best it's an extreme matchup fish, at worst it's a 6-0 if given a turn or two to set up.
As to the two mons being most seriously considered:
* Garganacl - major. This mon is much, much easier to kill if stuck with a mono-Rock typing, and would be the first ban where terastalization was the problem, rather than just a factor.
* Volcarona - moderate to major. It's literally the same complaint as the last four generations: sometimes it's dead weight, sometimes it's 6-0'ing a team. Terastalization makes it more effective, but a couple of its defensive checks can exploit the mechanic, too, and its strengths are compounded by Dexit and limited Toxic distribution.
That's eight bans where terastalization wasn't a factor, three where it was (two of which are likely bans anyway, the third is questionable), and two potential suspects where it would be a factor. Calling this an 'endless loop of bans' due to the mechanic is flat out dishonest.