I definitely can get behind Rotom-W moving up to S. That thing is the face of quite possibly the tier's most dominant playstyle in VoltTurn, and is fully capable of fitting comfortably onto multiple other team archetypes. In general, Washtom does really well as a check to tier staples like Infernape, Scizor, Mamoswine, and Gliscor lacking Facade, and has really good offensive synergy with a large number of defining offensive threats, particularly those previously mentioned. It has a surprisingly amount of versatility and flexibility between its many viable sets, which include defensive, specs, scarf, waterium z or leftovers, and even Psychium Z to lure in Amoonguss. The influx in usage of Seismitoad and Gastrodon is testament to Rotom's influence, and overall I definitely see it as more centralizing and defining of a Pokemon in comparison to anything else in A+. S rank material for sure.
As for the rest of the viability rankings, the upper subranks look solid, though I think some housekeeping is needed for ranks B- through D. Here are the rises and drops that I'd be most interested in seeing happen:
Cofagrigus up to B
This thing sticks out like a sore thumb in B-, considering nothing else in that entire subrank is capable of winning from matchup alone. With its OTR set, Cofagrigus is capable of nabbing setup opportunities against the likes of Infernape, unboosted or utility Cobalion, Mega Aerodactyl, Gliscor, Mega Beedrill, and several other threatening physical attackers. Upon entering Trick Room and boosting up with Nasty Plot, it becomes near unstoppable, and is capable of straight up 6-0ing a large amount of the tier's common offensive builds. Given that pretty much only Blissey and Alolan Muk can avoid the 2HKO from +2 Shadow Ball or HP Fighting after rocks, and that plenty of prominent physical threats act as setup bait for Cofag, it is more than worthy of a rise out of B-, where it truly doesn't compare to really anything else in terms of consistency and potency.
Slowking down to C+
Slowking still has use as a check to things like Mega Latias and NP Ape, though a lot of recent metagame trends have really been out of its favor. Mega Sharpedo and Specs Hydreigon are as dominant as they've ever been, while VoltTurn is at its peak with Rotom-Wash and Mega Manectric now in the tier. Overall, Slowking struggles too much in a metagame filled with VoltTurn and offensive Dark-types to maintain its current rank, and can even be powered through by some special attackers that it'd try checking, like Thunderbolt Mega Latias, Electrium Z Latias, Togekiss, and Starmie. A drop to C+ is justified right now.
Darmanitan up to C+
Despite the meme wars that emerged from this nomination, it is still something that I think should go through. Mega Latias and Rotom-Wash's introductions to the tier have kept Choice Band Fire-types like Infernape and Entei from spamming their Fire-type STAB as easily, though by virtue of its higher Attack stat and Sheer Force, Darmanitan is fully capable of powering through the aforementioned Fire-resists in just two hits. Due to the newfound increase in distinction between Darmanitan and Entei, I feel as though ranking them closer to one another is justified, and that due to the utility of STAB Sacred Fire, Entei doesn't deserve a drop, which makes rising Darmanitan the more logical option (I also just think its more consistent in its role than things like Salazzle and Tornadus).
Rotom-C up to C+
Mowtom is usually outperformed offensively by Rotom-W, though its ability to break past bulky Water-types a lot more reliably is enough of a boon to justify C+ in my eyes. It takes advantage of the increased viability and usage of Seismitoad and Gastrodon while more adequately pressuring Suicune and opposing Washtoms than Washtom itself. The 4x resistance to Electric-type attacks can also prove useful in reliably switching into opposing Rotom-Ws in addition to taking on less conventional Electrics in Magneton and Raikou, and is just one more niche this thing has over its main competition that for me, justifies slightly higher placement.
Porygon-2 up to C+
Lots of potential rising from C going on here, though I promise this is the last one. P2 is a generally unexplored mon, which is why I think only rising one subrank is justified for now, though staying in C when its Z-Conversion set has proven to be lethal against a lot of top tier threats is quite the injustice. It can be difficult to set up at first, though once it's boosted up Porygon-2 can easily take on Cobalion, both Latias and its Mega Evolution, Weavile, Mega Manectric, Rotom-Wash, and just about anything else in ranks S through A-. Download and Recover are two really useful tools it has at its disposal as a sweeper, and considering that it's fairly easy to build around and means of revenge killing it are limited, I absolutely think that C+ is a good starting place.
Venusaur down to C-
I'd like to start by saying that I'm not knocking Venusaur's sweeping capabilities under the sun. It's actually really potent and can put in work against even stall with Z-Power Whip (thanks for the recommendation Sparrow). My main gripe with Venusaur's current rank is that it shouldn't be the same as Ninetales's. Ninetales is a very capable wallbreaker due to having Drought, and as a result it isn't limited to only functioning on sun builds. Venusaur, however, requires the support of Ninetales to be functional in its role, and as a result is much harder to fit on a team. Due to its potency under the sun, a rank in C- is justified, though being ranked alongside the Pokemon that it
needs to be useful in a match but can also be useful outside of specific archetypes is something that I don't think makes C reasonable anymore.
Stoutland and Whimsicott unranked
This is getting a tad bit boring, so since I think these should both just go the same place, I'm lumpin' em together :P Anyways, I love me some Stoutland, but it's literally only functional on builds with Hippowdon or Gigalith, which is falling off lately in the case of the former, and is almost never used in the case of the latter. It also has problems against the tier's plethora of Fighting-types, Mega Aggron and Steelix, Alomomola, and especially Doublade, which is beginning to see both more viability and usage due to its good matchup against several top threats. As for Whimsicott, well, it sucks lol. The only niches it has over any other offensive Grass are its high Speed and Prankster + Encore, though those don't distract from the fact that it's piss weak even with a Life Orb/Choice Specs and is outperformed as a result. It's really a shame since this thing was so fun to use last gen, but nowadays it feels like it just sits there during matches and waits to die. Maybe C- is fair for it, but getting unranked entirely is definitely on the table in my eyes, since I haven't even seen this thing win a game since beta.
If you made it through this whole post, thanks so much for reading! I hope you guys enjoyed, and let's hope for some more discussion before this next update! :)