So, I think there are some UU Pokemon that also deserve a spot on this list unless I'm mistaken.
The biggest, most obvious candidate is probably:
If you want to play an anti-weather / non-weather team, or you just want to troll Rain players really really hard in this metagame, Kingdra is probably your go-to guy. Basic story... if Ferrothorn goes down, GG.
Well, that's not true... Kingdra has problems with Tentacruel, Gastrodon, Vaporeon, and Special Defensive Jirachi too, but offensive rain is so prevalent, and Tenta/Gastrodon/Vappy/Jirachi don't exactly want to keep switching into Specs attacks from the wrong end the whole game (Jirachi especially doesn't WANT to switch into a Rain + Specs Hydro Pump).
And yes, I'd promote Timid Specs Kingdra as the best Kingdra set for OU now. Sure, that's because in part it seems a lot of players don't KNOW that Kingdra can out speed and OHKO their Rotoms and Brelooms. Sure, that's because a lot of people don't KNOW that Kingdra can OHKO their Hippo or Skarm, and don't instinctively switch in a very, very, very, rare Blissey. Also people tend to let their ferrothorn die way too easily, just because it got up a layer or two of hazards.
outspeeding and OHKO'ing Tornadus, Thundurus, Keldeo, etc. and OHKO'ing them (2hko in Keldeo's case...), and also packing bulk comperable/better than Rotom-W... rain teams find themselves on the wrong end of the reason for the drizzle+swift swim ban.
And it's not like Specs Kingdra is dead weight against not-rain. It's very anti-weather in general.
Sun Teams tend to carry very few steel types, and have a very hard time dealing with 4x Fire Resist + Specs STAB Draco Meteor.
Against sand... well bulky, fairly fast, super powerful STAB water attacker is of course useful against them too.
True that against other non-weather teams Kingdra's nothing special, but it's hardly dead weight either. Well worth it's ass kicking on rain and good use against sun and sand. Plus, you could always pack your own rain dancer... never a bad choice in this meta.
Plus, it can add a whole different dimension to your Drag-Mag team.
I'd say Kingdra could take a
spot in C for being incredibly useful in the right situation, or with the right support. At least a D rank though for sure.