my opinions on some noms:
mega metagross ->S: agree, using this with tapu lele is fucking broken, there's no switches to this thing, and now with psychc terrain allowing you to 2 shot lando-t with zen headbutt the 4mss from last gen doesn't exist anymore, with zen headbutt/meteor mash/hammer arm/thunder punch you can just destroy anything that have an HP stat(fucking shedinja);
zygarde-10% A- -> B+/B: agree, it's a nice mon, but it doesn't hit that strong for a choice band user, it's mega frail and have a lot of switchs, definetly isn't on A- level of mon;
nihiliego A- ->B+: agree, it's better than zygarde, but so many things can overwhelm this, being locked in a poison move it's awful, my favorite set is offensive rocks with hp ice for luring, but i don't see it on A- level too;
A-marowak A- -> B+: Disagree, this think is a nice check to pheromosa, tapu bulu, magearna, char-x/y, celesteela, heatran, ferrothorn, mega scizor, mega venu, some buzzwoles, amoongus, toxapex, skamory, clefable, chansey, and every eletric type bar a-raichu and hp ground xukitree, every time this thing get in the field it's going to A: spread a lot of damage; B: use a utility move in SR/WoW;
gyarados mega B- -> B/B+ : agree, IDK how this thing is so low(lower than regular gyara and starmie, and being in the same rank with slowking and breloom) pheromosa and mega venu are pain the ass for this, but after a +1 this shit became rly hard to stop, if your using A-ninetales as a parter you will get the +2 becoming unstopableA;
A-Ninetales C+ -> B-: agree, aurora veil is super broken, also warning + freeze dry allow you to beat rain teams so easy;
A-Raichu D-> higher: agree, this mon is really underated, on rain + eletric teams this thing is a beast, being able to KO/2KO almost every with thunder/psychc/focus miss/surf(rip a-marowak and ground types) thing is awesome, weather and other terrains can't really stop it, tapu bulu/lele can't switch against thunder(bulu is KO'ed by thunder + psychc), ttar is KO'ed by Focus miss, hippo is 2KO'ed by surf, priority hurt it a lot, but it's definely way better than all the D mons, and most of others C-/C, i would say this is C+ worth.
my own nominations:
Xukitree C+ -> B-/B: i was really suprised to see this mon so low, scarf/z-hypnosis is decent against offense, but the set that really deserve the rise, is tail glow + 3 attacks with z-eletric, jsut demolish any kind of stall/balance team, just click tail glow, and than see things dying, i underst that offense is rly bad for this, but there every mon that is slower than xukitree is wrecked by this(bar shedinja), definetly should be in the same rank as togekiss.
crabominable/wishmashi ->unraked: what this things are supposed to do? i don't think that trick room is that viable at all, this are probably going to be removed in the first "we revamped the lower tiers, because there were a lot of gimmicks mons"