Yeah dragonite is in no way anything less than B+, it's perfectly fine where its at. While the rocks support is pretty annoying, offense has a pretty tough time preventing set up from dragonite, and dnite can also own all those priority offense you see that use talonflame/weavile/bisharp/breloom to revenge kill stuff by just clicking boosted espeed. There are some common stuff that needs to be weakened before dnite can sweep, like clefable, ferro/zor (if eq), tran (if fire punch), lando-t, and ttar.
While they are pretty common, they're not too too hard to weaken or lure or just trap with zone, and this is just the DD set. CB is a pretty hard hitter that can function as a revenge killer with banded espeed, and there are some weird sets like bulky roost dd which pretty sure bengy used
here in SPL, and some rare mixed sets with iron tail or DD weakness policy (which isn't as bad as people say) can surprise people too. Dnite is fine where it is.
Gatr and diggersby are both strong and can put in work against the builds they're supposed to, I can't really see them in the same tier as mega beedril, dragalge, and victini. They're better than that. Swords dance Aqua jet Gatr is also a pretty cool set, although even more strapped for coverage between ice punch, crunch, and superpower.
Reuni and tangrowth should definitely move up, tangrowth especially runs a great av set with giga or leaf storm / knock off / and hp fire/hp ice/eq/rock slide in the last two slots. You can tailor it to check what your team needs to beat/lure and its just a great not-passive fatmon in general.
Manectric Mega should not move down, while sand balance and mega lati is pretty annoying for it, I find it pretty hard to justify that "prevalence of priority" is wearing it down when it is beating most priority users anyways (think talon, breloom, weavile, azu, scizor, dnite if rocks). Coincidentally, not much sets up hazards on mega manectric either. It beats every relevant spiker (klefki, ferro, skarm) and its coverage can beat some relevant rockers like lando-t or chomper. It's not awfully strong and hippo shuts it down completely but electric/fire/ice coverage with good speed and volt switch is enough to sit among the likes of mega venu, mega garde, and char-y.
Mega gyarados should also not move down, it is not easy to revenge kill at all. Even modest scarf keldeo only has a 6.3% chance to OHKO uninvested mega gyara, this thing's bulky as shit and getting up 1 dd is no problem, even 2 is pretty realistic. It has common checks, but those common checks are also pretty easy to weaken and lure, and mega gyarados itself can check some relevant stuff like excadrill. Taunt+DD also shits on some fat builds really hard.
Finally, I want to make a nom of my own: Raikou to B+
Raikou has seriously taken a hit these past few months. More and more sand balance, more mega latias, more ferrothorns to set spikes and more scarf tars to keep them up, the metagame is seriously unfriendly to raikou right now. Don't get me wrong, calm mind+volt switch is still a lovely set and its still a great check to torn-t, gengar, and thundurus and the like but meta trends are really against it. It was used only 17 times throughout all of OLT playoffs and it's been used ONCE in spl so far. I can see it chillin with celebi, gastro, and heracross-mega, it doesn't belong in A- anymore and it should move down.