S:
As the only type that doesn't really have to play the hazard metagame with strong versatility in team options, Flying is still the best type in the tier in my eyes. While it had a mediocre MPL I think that came down to a lot of people sticking to comfort builds (we saw a lot of Glisc + Corv + Torn-T with some combo of DNite, Lando-I, Molt and Cuno while everything else fail to crack double digits) and not really trying to do much interesting with the type overall, instead being compliant. Once people start doing cool things with this type again, people will realize its the best again.
There is a reason this type had the best MPL overall, its sheer power without any majorly glaring weakness outside of a poor MU into hazard stack (which it can generally handle through just putting on so much offensive pressure since even its defensive mons have base 100+ in their offenses) keeps it high for me (I do jump a bit between this and flying being No.1 though)
With this type getting further optimized again, it is just a great offensive type without many flaws. Especially as Fairy and Fighting are not proving to be perfect answers into them while in response, Dark can just put on near uncontested offensive pressure with really strong hazard support in Ting-Lu which also gives some defensive stability. Like Dragon it does lack hazard removal and unlike Dragon Sableye and Mandibuzz (the main defensive mons) aren't offensive super stars, but its got too much gas not to put this high.
A:
I think Steel has a similar issue to Flying with a lot of people sticking to the same 5 core + filler mon with minimal experimentation, but it being the best type in the tier to hazard stack with thanks to Ghold is valuable. Also resisting like everything as well with a good MU into most types is solid.
Ground is Ground, I think this type is just too consistently solid of just being able to click buttons and get away with it. Yes its got some problem MUs, but physical attackers clicking STAB Earthquake will never be bad in my opinion unless the metagame becomes so Grass, Bug, and Flying focused. But that won't ever happen.
Similar to most types, bad hazard game, but unlike most types it is forced to deal with said hazards as a problem which does hurt it. Still, its got strong versaility, a buffet of viable playstyles, and just so many good all around mons, its still solid.
Same thing as ground, STAB Close Combat is too good. Unlike Ground this is a type that does have to worry about a few bad MUs that are incredibly rough, but having those good matchups into most of the top 5 (flying is a bit iffy but still plenty playable) is what keeps this type in competition for me.
These types are kind of just the same to me. Both just want to click their strong special attacks with like one insane physical attacker to push them further. Why I put Ghost as B and Fairy as A is due to how much stronger Fairy's STAB is along with Klefki granting a nice boon. Not having to worry the world's worst mirror and having a good Dark MU and better Dragon are also nice boons.
B (proper now)
read above.
Sun offense is dumb. I do think Sun enabling 7 turns for so many breakers as a whole is stupid and has so much breaking potential mostly kept in check by Dragon having an easy time using proto to throw it right back in Fire's face and being a constant presences along with Ground and Water always keeping fire on its toes.
I'm a believer in Bug, always have been. This type just gets to do whatever it wants a lot of the time because of how good its sticky web offense can be. Of course it can struggle into stuff, notably Fire's recent rise, along with Steel still remaining a consistent defensive hold prevent it from pushing too far. But Bug is my pick for most underrated type.
C: From this point onwards I think the types are very much not consistently good and a bit more of a matchup fish. That being said they have strong enough tools that into most matchups they can reasonably work.
Bias on main, I still think Poison has a place. It can beat nearly every type outside of Ground, Flying, and Fire reliably (and Fire I'm not convinced is a lose if you MU fish it correctly) but really has to choose its matchups in the builder first and foremost and nothing really feels like it covers enough leaving major blind spots. Still consistently strong Fairy, Fighting, and Ghost (thanks AMuk) with generally a solid Water and bug makes this the best of the fishing types.
:Blank-Plate: First off, I did not know until doing this that normal got a plate this gen. (Still needs to be implemented, but it exists) Secondly, normal has some weird MUs, like its got a generally great stall matchup, has strong tools to break most types since Ursaluna hits so hard making it rough to switch into and the Ghost immunity really pisses of, well Ghost, as it prevents Hex Spectrier and Ghold from going super nutty but in the same vein doesn't enjoy seeing Fighting or Steel at all.
This one (and psychic) might be questionable, but strong Dragon, Flying, and Ground does it for me. Yeah its got some disasters in Steel, Bug, and Fire but when it works, oh god it works.
It has A strong fighting matchup and can do some decent work into Flying and Water. Maybe this type needs more cooking as I know Neko is cooking something (because no one else wants to build Psychic) but I don't think its completely booty, unlike the last three.
D: Don't, I don't think any of these types should be used unless you want to CTeam and even then, they're bad.
The only type here that can fish correctly. Its ability to actually beat Fire and possibly put pressure onto Flying (but I've seen so many good flying teams consistently handle it) makes it the best of the worse. Still kind of just collapses to most types those. Doesn't even have a bug MU worth trying to salvage.
I think its got a Steel MU, probably claps Water real bad and might have a flying? Still Dragon and Ground stop this from being anything too good and it lacks any sort of good response to special spam which can allow Ghost and Fairy to easily blow it over.
Meet potential type because there is no good reason why people keep loading it, thinking it might get anything done, when the only accomplishment its gotten recently is winning against itself in MFPL. That is it. It got loaded thrice in MPL last year to no results, once this year to no results. It will happen against next year when people try to fish and fail with it as per usual.