Wanted to make some nominations, I don't play ubers too much but I wanna get involved more in this tier, and wanted to share some thoughts, every critique is accepted, so feel free to not agree with any of my nomination.
Arceus Ground to A+: From what I have played ORAS ubers, Arceus Ground is a monster, it beats Groudon Primal quite easily which is the tier's top threat, it beats Salamence with Ice Beam which is another big threat and it beats Lati Twins too if they aren't carring Grass Knot (which isn't super common from what I have seen). Definitely a big and relevant threat in the tier, being able to check the many of the most common mons and to put some nice support to the team which is running it (I guess a set with Will-o-Wisp, Defog, Recover and Judgement is something to consider too, even if ofc the Calm Mind one is the most dangerous, I haven't tried yet the Sword Dance one but I thin it can put some work too).
Arceus Dark to A+: That thing is a monster too, the Calm Mind one with Refresh especially beat Stall by itself if Xerneas is weakened which is a very big niche. It beats Lati Twins, and nobody in the tier wants to switch on this thing not named Xerneas / Arceus Fairy (which from what I could see isn't too common, people tend to prefer Arceus Normal, Ground, Dark and Rock mainly). Definitely a big threat imo, that deserves to rise. I can see it also in S rank in the future for how strong it is and how difficult it is to stop it, but A+ is already enough for it as of now I think.
Genesect to A-: In ORAS I think it had an huge boost with Lati Twins raising in usage thanks to Soul Dew since it's one of the few mon that can switch-in on them and gain momentum with U-Turn, it can also beat Mewtwo and Mewtwo Y, Darkrai, weakened Arceus Dark, Gengar and revenge-kill Salamence and Xerneas. Obv Im talking about the Scarf set which is the most consistent imo, as Edgar's most recent RMT shows. I think that beating / revenge-killing all these threats for one mon is a huge niche, and Genesect is really good at doing this, and as well as gaining useful momentum for its team. In my eyes it deserves a rise.
Lucario and Kyogre to B-: I won't spend too many words on Lucario but I agree that it deserves a drop. In XY it was good just because of Sticky Web but now that Latios and Latias got that buff, it isnt too hard to defog it away, also it got competition as a mega with Salamence, Diancie and Metagross which are, especially the first two very good atm. I believe that Kyogre deserves a drop as well, I mean I know it was an huge threat in XY but now it's just outclassed by its Primal forme imo. Scarf and Specs set can't be used with efficacy because of Primal Groudon which is in EVERY team and give free turns to Groudon isn't the best thing to do, especially since its Rock Polish / Sword Dance / Double Boost sets are rly threatening and not so easy to stop. Also, its CM set it's outclassed by Primal Kyogre which has better SAtk and can actually beat P Groudon with +1 Blizzard. I can see the reasons why people would want Kyogre to be still a B threat because it's itself a really good mon, but P Groudon being the most common and the best mon in the tier, doesn't allow Kyogre to shine at its best and also the presence of Primal Kyogre makes things worse since from some points of view it's better than regular Kyogre (I'm mainly talking about the CM set).
Ditto to B-: Xerneas, Mega Salamence, P Don, P Kyogre, Extreme Killer Arceus, Darkrai. The Uber tier is full of setup sweeper and Ditto takes advantage of all them, and even if it isn't as good as it was when Mega Rayquaza ruined the tier, it's still a really good mon to have in a offense team imo, being able to revenge-kill the major part of the setup sweeper. Can't really see it in the same rank as regular Diancie and the Charizards. Imo it needs a rise.
I guess that's all I got. My uber experience isn't the best, so feel free to comment in anyhow, hope to bring some interesting discussions in this forum!