Was it??? People have always complained about Valiant being too strong, too quick and too versatile. Coming up against a Valiant has always had a "let's spin the wheel and guess what one of 50 different sets it can run": is it Specs, Booster CM, Booster SD, Scarf Trick, Mixed Life Orb and this is before it Teras which it doesn't really need to anyway.
In the context of gen 9 power creep, yes. People complain about everything. But it's more common since the gen came out for people to suggest Valiant isn't broken or even that it is healthy for the tier, at least in my observation. I don't go to this forum every day, though, so maybe I missed a bunch of complaining about it?
Either way, I'd bet most people wouldn't want to ban it before and after the sleep saga.
Now out of these mons, how many are actually broken because of Tera? Annihilape Tera Water, Espathra Tera Fairy/Fighting, Regieleki Tera Ice, Volcarona Tera Anything and Terapagos Tera Stellar. Out of all those bans only a handful were actually because of Tera, maybe the problems were exacerbated with Tera but at its core the mon was still problematic.
The problem with this is it is still quite a higher percentage than you make it sound. Add Roaring Moon to this, as was brought up before. That's 6 out of your list of 18, which should be 19 with Moon. 6/18 = 1/3. So you have roughly one third of these bans being tera related. Technically a little less. I don't care to find if you missed anything else. Roughly 1/3 on nearly 20 mons is enough data to come to a conclusion.
My original point talked about
only two pokemon primarily being responsible for the sleep ban. That is Darkrai and Valiant. Tera is responsible for at least 3 times that, right? And more bans are likely coming because that's what gen 9 with tera has been.
I realize the sleep argument is more nuanced than that, and you also have concerns such as yawn + hazards, but you can see the clear double standard here if we just count the mons. If mechanics are overall problematic, we pick and choose based on preference which ones we ban or not. Not by balance or competitiveness. To save Tera, we pick the mons. To save Valiant and hazards, we pick the sleep mechanic.
I also don't vibe with this point because yes, Dynamax was clearly broken and yes people like Tera more because it is nowhere near as broken and has more uniqueness to it - it's not just because "it's fun" it also is competitive to a lot of people otherwise we wouldn't even be having this discussion.
It's not relevant whether one was worse or not. Flutter Mane was worse than Chien-Pao, but Chien-Pao was also eventually banned. Rightly so. Gen 9 is the one with the most OU bans in history. Maybe gen 8 would have looked like that or worse had we kept Dynamax. Even if it would be worse, that wouldn't make gen 9 better.
I also don't vibe with your point because of the clear double standard. I can make arguments about how it was nice that Dynamax provided another way of setting or changing terrain and whether. These are competitive uses. No one would say that it is enough to keep a clearly broken mechanic. But with Tera, people like you try to minimize and deemphasize the clear brokenness and emphasize the niche benefits. Sure, Tera is a fun mechanic. Is it competitive? Heck no.
Even draft leagues tend to only allow lower tier pokemon to tera, if at all, because they know how blatantly overpowered such a powerful mechanic with no drawbacks or opportunity cost is. Yes, I know draft league is an entirely different format than OU. Don't @ me about it. Tera breaks everything is my point. They don't allow the actual good mons to Tera for a reason. In OU, we simply add the tera bonus multiplier to our ban list.