Speaking of late comers, why are Solgaleo & Lunala A rank anyway?
Like, yes, legendaries, those are good. But when you get them there's what 6 battles left? And a treck through ice country but that's trivial. By that point surely your team is all set and ready to go right? I don't know, maybe it's just me.
Both of them have really good attack and special attack, are bulky, have decent speed, and have access to a wide spectrum of offensive moves, and the kitchen sink of defensive moves: Morning Sun/Moonlight, Cosmic Power, Work Up/Calm Mind, dual Screens, etc. So basically by E4, if there is any role in the team that need to be filled, or if one of the pokemons on the team struggle to keep up, Solageo/Lunala will most likely be able to fill that spot. Also, availability is late, but you always have to catch it anyway so it basically comes for free.
That said, Lunala is quad weak to ghost and dark, so some care is needed for Acelora.
On the same note, I would advocate to
move Zygarde 50% down to B. Here is the reasoning:
1) If Zygarde 50% is obtained as soon as possible, then the only fight that it can make a significant difference is against Nanu (using Break Bricks), however as discussed previously this requires a non-trivial amount of backtracking/bookkeeping. It can also contribute against Guzma, but I am not convinced that the fight is hard enough to tip the balance.
2) Post-Nanu, Zygarde 50% is not having a great match up against Lusamine's clefable (if you are able to obtain it around Aether), and do not have any SE moves against Kommo-o. It will do okay against Hapu, but it doesn't have the best match-up ever. During E4, its 4x weakness to ice, shallow coverage, combined with its speed-tier doesn't make it that dominant (it is no Garchomp...). For something coming this late, I expect better.
Similarly,
Zygarde 10% should move to C. As others said in previous posts: it's a stronger dugtrio that comes later.
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Edit: that said, zydog is still best dog in my heart.
Edit2: The problem with zydog is that it really just want a Choice Band to spam thousand arrows, but in-game you only have access to plates and a life orb...
If you need to put so much emphasis on somebody's sweeping capabilities, you know it's not the best Pokemon. How many buffs do Wishiwashi and Archeops need to OHKO things?
But Mimikyu's not even that good at sweeping. 90 base attack is on the low side (Colonel M literally told people who think Blissey's 75 sp. atk. is bearable enough to leave the topic and refrain from partaking in the discussion, and 90 isn't much better), and 96 speed no longer outspeeds everything in the endgame, especially on a latejoiner with a level disadvantage. The bigger issue is its coverage though - the strongest move is the 70 BP Shadow Claw, and its "coverage" is just Leech Life/X-Scissor (you do want to use the former) until E4 when it gets Wood Hammer and Play Rough.
Having Disguise means that its attack is effectively at 180, since it always has a sword dance. You also get a red card earlier in-game, which means that is can set up sword dance and force a bad match-up to switch.
It is a much more delicate tool to use than the usual "select attack => things die". I agree however that coverage and speed are real liabilities.