Chansey dropping is pretty long overdue, I supported its drop alongside Skarmory's a while back, and I still feel like that was correct at the time, but Skarmory has undoubtedly gotten better since then, what with its ability to deal with physical spam teams with a Shed Shell equipped (that is until Knock off Pinsir takes off on those kind of teams). Chansey, on the other hand, has gotten worse if anything, for reasons that have already been explained. I just don't see it on stall anymore, or at least not nearly as prominently as Skarmory, Jirachi, Doublade, or Starmie. For that reason I feel like it could drop down to further to B though it's arguably better than a few things down there (looking at you, Quagsire). But I really don't think it's as good as anything an B+. In any case, it should definitely be dropped to B+ for the time being.
Speaking of Starmie, I'd like to go back on my nomination for it to move at A-. (please note that I will only be discussing the defensive set here) After further testing, turns it's not as reliable as I thought it was. The problem, oddly enough, isn't Gengar (who does get worn down by Scald and can be outlasted by Starmie without too much difficuly), it's Doublade. Doublade just completely stops Starmie from doing anything at all, even has Rest so it can't get worn down from repeated Scalds and guarantees rocks will stay up on your side of the team. This is especially troublesome given that Starmie is supposed to be used on stall, a playstyle which cannot apply enough offensive pressure on opposing stall teams to stop rocks from going up in the first place. And if we assume that Doublade is on every stall team (which is not necessarily an incorrect assumption) and that Starmie and Skarmory are the only relevant hazard removers for Stall (again, not far from the truth), a well-played Skarmory stall team will pretty much always win against an equally well-played Starmie stall team since it will have total hazard control and will have a much easier time forcing everything to die from switching repetidely into rocks, unless the Starmie team manages to stop rocks from going up and Deofog from happening which is obviously very difficult for a Stall team to pull off. Basically, Starmie is very good at spinning against offense, bulky offense, and balance, but completely falls flat on its face against stall, and although stall is uncommon in this metagame I feel like completely failing against an entire playstyle reason enough to keep it in B+
Magcargo I don't think it's fair to say that Landorus-I is a better wallbreaker than YZard simply because YZard has 2 very important things Landorus-I lacks. The first is a spammable STAB. While YZard can Fire Blast/Flamethrower and almost guarantee something will take damage, Ground immunities are common to a point where Earth Power can be a very risky move, potentially giving a completely free turn to the opponent. There is absolutely no risk in using Flamethrower since even if you hit a resist at least you'll have worn something down. (This also ties into the Keldeo v Landorus discussion we had a while back)
The second one is recovery. Recovery may not seem like something you'd want on a wallbreaker, but trust me, they tend to get worn down a lot when facing defensive teams and sometimes can't quite finish the job. Roost basically means that Toxic, as well as minor damage from resisted attacks or defensive Pokemon are far less effective on YZard than most other stallbreakers, who are basically on a timer to do as much damage as they can unless you provide (Healing) Wish, and this includes Lando-I.