Between my two alts I've played ~100 games of MnM the past two weeks (mostly just clicking while at work...) and want to contribute some opinions on my personal VR. All of the tiers are ordered alphabetically and I'll try to mention relevant items where I feel they fit. Viewer discretion is advised.
S:
Nothing. I agree with the VR as it is now, not any one mon stands out above the rest!
A+:

- Altarianite and Pinsirite are both equally devastating

- I think Sablenite is the best option but regardless of item it is quite annoying to handle Salt Cure chip

- Latiasite is borderline A to me at times but it is a very effective defensive pivot into a lot of ESpeed stuff and
pyu sold me on Grass Knot the other day in the OM room which is actually super nifty

- Although my own success with Diancite sets was kinda mixed, Gia certainly proved it is a potent offensive threat. Gyaradosite is really splashable and Latiasite is okay as well

- Altarianite and Glalitite are both equally devastating, it's also a great pivot to get other mons into good spots
A:

/

- Lumping these two together, Ground is a nice offensive threat and Water is a great defensive mon

- Not much can take a +2 Lucarionite Poltergeist and it has plenty of teammates that can get it advantageous matchups

- Life Orb sets are really tough to switch into and Rocky Helmet is one of the best ways to deter Urshifu from clicking buttons

- Defensive and offensive sets are equally effective, with Pinsirite standing out as one of my favorite items overall

- I am Hippo-pilled, I love Sablenite Whirlwind sets so so much in this meta

- Deceptively strong breaker that struggles to hit the field at times but can blow stuff up like few others

- Lucarionite sets are one or two clicks away from just taking down every mon that isn't an ESpeed mon (I click Volt on the Dragonite because I know it's clicking DD...)

- One of the trickiest mons to manuever around, Metagrossite RS is so strong
A-:

- Intimidate is sneaky good prior to using your Mega and then it has two great choices in Altaranite and Pinsirite, to go along with Morning Sun as well

/

- Ghost is strong, Fairy is great offensively or defensively, good mons

- Altarianite Entei (Adamant especially) is really dynamic into a lot of standard Magearna + Urshifu teams

- One of the premiere defensive pivots that can also use Whirlwind to great effect, good mon

- Another excellent defensive pivot with a ton of utility, Aggronite sets are quite good

- I could maybe argue Aggronite Zama to A but the combination of that + Lopunnite fit fine in A-
B+:

Metagrossite Iron Boulder is deceptively strong and Milotic is pretty good at defensive pivoting and anti-setup
B:
B-:
