Take all this with a grain of salt cause I haven't been able to PvP much myself lately and I'm prone to missing some details.
As far as azu goes I could give points either way. Its belly drum set keeps getting harder to use especially if you don't have something like screens support to back it up but it's still a monster and incredibly hard to switch into. My personal bias would point me towards putting it in A+ but I could just as easily see it in A.
For gengar I think you summed it up nicely, I would probably drop it to A- but it still has its main traits in being really fast hitting really hard with good coverage and having some nice utility moves although all of those are slowly becoming less potent.
I think kabutops is definitely better than ludicolo and overall slightly worse than kingdra but idk if that's a fair comparison cause both are the best rain monster on their respective side of the offensive spectrum so I could see them being in the same tier. You don't usually ask yourself which one of the two am I going to use cause you can just run both.
Diggersby is a cool Mon with great potential that I'd love to try out, until I do I don't think I can really judge it.
After gen 7 I'd maybe swap will o wisp for toxic on jellicent. Before it could counterstall just by using the combo of taunt and burn and the occasional scald but with the burn nerf that doesn't work as well when the opponent has lefties and I feel like toxic would make it much better at stallbreaking while still keeping the option to burn opponents with scald although a more reliable burn would help more Vs offensive Mons.
I'd also move smeargle up a tier. Although that's probably mostly because of my personal experience with the Mon. It's by far the best sticky web user and the only reason the playstyle is viable imo. Having access to spore only makes it easier for your setup Mons. I understand if you disagree because I'm saying this cause I had great success with my hodgepodge of a sticky web team and that was a few months ago.