Hey, wanted to throw in my thoughts, relatively similar to Mushamu so I won't go into depth except for specific changes. Split mine up a bit more to better give my own reflection.
S
Flying - Agree with everything mushamu said, most verstaile type other than perhaps water and can pretty much beat anything including ice with double steel move Cele and Zap Galar. Access to a versatile attacker and an electric immunity in Thundy T and of course Broken Bird destroying teams along with a solid fire switchin with Dragonite and Landorus-t always one of the best competetive mons. Excellent synergy among the type and with the introduction of HDB in SS it has certainly become the best type in my eyes
A+
Ground - One of the best offensively oriented types in my eyes and whether running sandless or not both work extremely well and have access to a solid water immunities. The main thing pushing it over the edge to me is the utility of sub landy gravity set-up setup which has a myriad of uses as well as the popularity of AV Mamo allowing a decent check to psys and Kyurems.
Water - As aforementioned probably the most verstaile type in the game with a huge variety of options in the teambuilder beyond just rain vs non rain water. Urfishu has certainly improved the type exponentially and the vast variety of building options such as stall, rain water, balance, and even more offensively oriented water all work well. Has access to excellent mons such as the king toxapex, crawdunt, rotom, fini, ect.
Steel - Great type with an excellent selection of mons lot of threats as mentioned but can be played ard if done right and stuff like scarf heatran can help quite a bit especially with the flying matchup.
Psychic - One of the more technical types to play but it has an excellent variety of mons with varying sets such as sub tini, hatterne coveres alot and lele is excellent speed control along with good bulk in bro and solid rockers in rachi/zong. Tons of variability and can beat most top tier types if played well.
Ice - An excellent anti-meta type that breezes through many of the top types specifically due to kyurem and with the rise of arctozolt I think it deserves a spot in A tier, good momentum with darmanitan and Ninetails excellent for screen setting and the dark matchup.
Electric - Probably the best offensively oriented type in the metagame with access to constant volt switching around and excellent mons to take advantage of this such as relegeki, zapdos, or zerora. A very fast and strong hitting type that does well against most high tier types as well.
B+
Fire - Fire is also a solid anti meta type that has a good variety of mons but lacks any strong defensive core, it's all about offensive pressure. Marowak alola is underrated as hell in my opinion as it is an excellent wallbreaker that covers electric teams and with mons like cinderace, sun setting capabilities, and good speed control its a very solid type.
Fairy - Fairy was definitely one of the top types especially with the attri fairy team becoming so popularized but as time has went on a think the type has become slightly less viable especially with the rise of steel. Still it has an excellent selection and with screen setting and the tapus you hit nearly everything. Certainly harder to play than it used to though.
Dark - Don't play much dark so don't have a ton to say but its a solid type mons like weavile and zarude along with screens setting make for a good hyper offensive playstyle and balance with sab works solid as well.
Ghost - Underrated type in my opinion has access to an excellent variety of Pokémon such as Spectrier, Froslass/Corsola for hazard setting, and good speed control along with an excellent sweeper in dragapult. A difficult type to learn in my eyes but can be very solid if played right
B
Dragon - Dragon definitely deserves B/B+ in my opinion, Access to kyurem along with kommo o allows it to beat many top tier types and dragalage with t spikes pressures the hell out of teams along with a solid rocker with garchomp. Certainly some variety but dragapult also pushes it over the edge in my opinion. An excellent scarfer that can turn out and provide momentum and fuck up psychic teams if played well. Downfall of fairy lately has also led me enjoy dragon a lot more although ice really is an auto loss but sub dreigon and such fucks up steel and overall I think if played right it can be excellent type.
Poison - Also don't play much poision but it has an excellent core that can be hella difficult for various types to break through, specifically water. Think its falling off a bit as people are learning to play around it a bit more
C
Grass - Hard type to play/build and mostly fishes for matchups as mentioned but I've seen some excellent grass games and rillbaboom itself i just a menace and it has a decent defensive core with cradily/ferro and solid setup sweepers such as zarude/Deceideye.
D
- Agree with everything Maroon all three types are extremely hard to use this meta with the top types pretty much destroying all of them but with that said but my one change would be Normal to D as well. It was an excellent type in ORAS and I think its unfortunate it fell off so hard but I would almost never risk bringing normal to tours personally. Ditto's cool and all and Bewear can put in hella work if played right but overall theres so many strong wallbreakers this generation the defensive core just doesn't work as well especially with the prevelance of knock off everywhere, as well as close combat everywhere
