I wish to first start by echoing seth's sentiment about the tier being in the worst place it has ever been. It is simply stagnant and unfun while also having the least potential future prospects ever. I also agree that Gholdengo and Dragapult should be given a second chance, which I will expand upon in a second. Having said this I believe starting a big unban wave is a bit preemptive, and should be only used as a last resort.
First of all, Darkrai should be banned. Darkrai has no defensive counterplay that cannot be either worn down quickly or muscled through via either a Z move or tera, forcing multiple offensive answers on every team, thus causing the tier to be far too offensive, something that I don't believe any reasonable amount of unbans will solve. Additionally, while I don't consider sleep as a whole broken, Darkrai is a perfect sleep abuser, having an excellent offensive profile independent of sleep, an ability that directly rewards it and an inaccurate sleep move to boot, further cementing its uncompetitiveness.
After this I believe Ogerpon-Wellspring should be revisisted. The tier has changed and is now almost unrecognizable from the time zama was around, and while Ogerpon is not very oppresive right now, this is in large part due to Darkrai. The rise of Kommo-o is largely due to Darkrai, as Ogerpon can run Play Rough to ohko it and there are far better answers to it. Scarf Urshifu being one of the best offensive answers to Darkrai has led to its popularity, and due to sharing many answers to Ogerpon, such as defensive Raging Bolt and Dragonite, while also easily revenge killing it, Ogerpon has been severely hindered.
These two are the only really obvious Pokemon that should be suspected, after which we have to just wait and see whatever else is broken and take action accordingly. However, should this not work out or should the bans not even happen, then the previously proposed plan is the only way fowards.
I personally voted ban on Gholdengo, though the tier back then was completely different than it is now. The current extremely offensive nature of the tier should be able to very easily handle Gholdengo, though as I stated previously I don't believe any amount of unbans will help balance, in fact Gholdengo could just worsen the issue by incentivizing hazard stacking offenses that can both easily abuse Gholdengo as a teammate and consistently overwhelm opposing Gholdengo through brute offense. Having said this I do support suspecting Gholdengo, as this is all hypothetical and would like to see its true effect on the tier.
Dragapult is the quintessential offensive Pokemon and would fit in perfectly in the current tier, both as a member of offense teams and as one of the most effective tools against them. Dragapult's legality in the tier has always been tied to Kingambit's, however I would like to first see it suspected alone before resorting to more unbans.
Kingambit is the one that I am most hesistant to suspect. The reason I previously voted to ban it was due to it being far too good at abusing tera. It had a wide array of options, such as Fairy, Flying, Dark, Fire, Water, Ghost, Dragon, etc., and the inability to know with certainty which of these it would be means one has to play around all of them at once, which alongside the usual tera/no tera mind game is in my opinion unhealthy. This would all be solved if tera were gone but mr smogon says no.
Hopefully at least one of these courses of action happens bc otherwise I truly see no future for the tier. Staying the way it is will just continually leak players until there really isn't anyone else that wants to touch this tier outside of ndpl for a ca.