I'm on mobile so apologies for being unable to respond with a post that has cool pictures and colors lolI think it's nice that you've put a lot of effort here AHappyCactus but there are actually a lot things I consider outright wrong here or they just aren't recent additions to the meta game.
For one Mew hasn't dropped in usage the past two months it's actually got MORE popular. For the month of august Mew had a usage of 10.26575% in ou above 1825 and in September it had a usage of 11.42156% in the same category. Mew hasn't exactly fallen out of favour much in tournaments either it's still liberally used on tons of balance teams. Similarly Clefable is decidedly more popular at the moment and that's a fair check to jolly Medicham anyway. Unless you are running adamant on your Medis which has it's own issues like being slower than tons of important stuff in the tier like offensive Lando and Tapu Lele.
Tapu koko + Medicham is something we've had literally since Medicham was released. It was actually extremely popular upon release. This isn't new at all and shouldn't cement a raise on the VR for it now. It's also a lot more prediction reliant than you were letting on. Back when Dugtrio was around it was more important but it's still relevant now. It's basically a 50/50 between your opponent going to their ground type to eat the t-punch or staying in to wisp/recover and electric terrain is somewhat short lived. It's also an extremely telegraphed play. If your Koko immediately pivots out into Medicham and they have a solid Medi switch in like Mew most decent players are going to be smart enough to realise that you are running t-punch.
Celesteela Toxapex balance is again not a new thing. This is literally months old and also guess what. These teams do actually run Mew and Clefable a lot of the time. Neither Celesteela nor Toxapex are able to deal with Zygarde so if they aren't using Lando or Bulu something like Mew or Clefable is actually a likely partner on these teams. That goes double because they can also defog/setup rocks which is something Celesteela and Toxapex cannot do and again these CelePex users are conscious of Medicham and might decide to use Clefable or Mew just to deal with it. Mew actually appreciates having Toxapex on the same team because it absorbs T Spikes for it so again these are common partners.
I'm not saying Medicham shouldn't rise but I don't find these arguments compelling at all. Furthermore i struggle to see many reasons to use Medicham over something like 3 attacks roost Charizard X or Mega Pinsir. It's main advantage is not being rocks weak but I don't think that's huge enough to say it's marginally better than those two when they are better at breaking teams open. If Medicham ends up rising I would at least hope to see Charizard X rise as well.
I suppose I should have clarified where I meant Mew had fallen, allow me to do that now. I was thinking more in terms of A) Viability, where it went from A to A- and B) In tournament play. Just using snake draft as an example, it dropped from 18% to 10%. I didn't even look on high ladder for usage stats so that's my b.
Yeah I wasn't saying medi + koko is anything new so much as I mean it's hands are not as tied as they once were. Removal of duggy, drop in usage of zygarde, make clicking specs volt switch a lot less risky. Although there has been a rise in drill since those days, the anti lead set is countered perfectly by medi, as fake out to breaks the sash and you out speed the following turn.
I don't think medi should have dropped to B+ in the first place to be honest, I think it fits much better in A-
I'm not at all saying it is without counters, just that the very limited counters it has are not quite as hard to handle as they seem. Yes this does mean it requires some support from its teammates - as every mon does - but in comparison to something like Pinsir and Zard, I would say that the no weakness to stealth rocks is huge, as these two are obviously super weak to them. Another advantage is you have far Moreno versatility with medicham than you do with the other two. Thunder punch I talked about in depth, fake out is incredibly useful in its own right, zen head butt is reliable and strong STAB that can be terrain boosted, ice punch destroys lando, etc. The others are rather one dimensional. (For the record I also think Zard X should go up to a-, but I have far less experience using it in this meta so I'm not comfortable speaking to it)
As for prediction reliance... I'll give that to you. No Pokémon is perfect, medi isn't the exception at all. I just think that because of all that, it does justify a raise to at least A-. Lots of your problems with it are valid but like of course it's got issues. I'm not saying bring it to S rank, but I do think A- is a better place for it to be.
(I'd tag you but again, on mobile RIP)