I'd make the proposal to move Arc-Ghost to S-Tier; it honestly does what Arceus does better in some ways. For one, it fucking spinblocks, and is IMO the best spinblocker in the tier because it can actually wreck stall pretty quickly because +2 252 Atk Ghost Plate Shadow Force is just insane, and you have the defenses to get to +4 a lot of the time. It can be used to wallbreak early game, mid-game, or late game, and it has ES to pick off a weakened +2 Arceus since, dunno if I mentioned, you're immune to their ES.
I'd also really like to seriously suggest placing Landorus-T on the list. A lot of people honestly don't know how amazing Lando-T is in ubers. Superpower does ~88% to Arcues normal with a Life Orb and Adamant nature, while they do not OHKO you with ES at +1. In addition, you can Rock Polish and sweep teams late game when all the walls have been weakened (Hazards support + Lando is no joke). EQ does ~45% to Groudon, Superpower OHKOs standard Ferrothorn after spikes, and no one really sees it coming and it is an excellent defensive pivot. And hey, it can set up on choiced electric moves, which is always a plus. And no, it's NOT an inferior Groudon. For one, it doesn't change the weather if you happen to like rain. Two, it has Intimidate. Three, that Flying-type can come in handy in many situations. And finally, and probably most importantly, not many people really know what the hell to do against it, and almost everyone is surprised by just how hard it hits.
Lando-T for C tier AT MINIMUM.
edit: Why the hell is Gliscor above KyuB? Gliscor has a hard time switching into, oh I dunno, most of the tier, and in addition it is walled by anything immune to Toxic. Kyu-B has some serious flaws too, but as a Scarfer, its niche lies in having a higher Attack than Zekrom while also being faster than it, which is critical at some times. Gliscor for C (hell, D tbh), Kyu-B for B.