Putting Primal Groudon above S+ rank is absolutely ridiculous. It is more than possible to make a team that can't be improved by Primal Groudon (as I already have). I don't really care if Primal Groudon is S+ or at the top of S, as the difference is minimal and the latter would not offend me nearly as much as it would offend some of you. I would have more to say about this but then I would be warned for "mini-modding" or some other arbitrary rule. Needless to ay, SuperSixFighters gave a reasonable explanation as to why he believes Primal Groudon to be S and not S+. I've long held that Xerneas is still the best mon in this meta, but to each his own. Just because someone's opinion is different it doesn't mean their "understanding of the meta" is automatically poor.It is less about the inherent qualities Primal Groudon brings to the table but rather how staple its inclusion is upon any archetype, relative to every other Pokémon in the tier. This contrast is so stark that I could argue with greater ease for Primal Groudon to be placed in a rank above "S+" in a rank of its own (under Mega Rayquaza and above "S"). This is because it is just that much more necessary for any ORAS Ubers team, compared to the likes of Mega Salamence and Xerneas, to carry it, to the point where the slim dichotomy between the "S+" and "S" ranks may render the upper echelon of this list misleading to fresh eyes.
(The fact that Ditto is still C- is an utter joke, but I've long given up any hope in fighting that battle)