You are wrong my friend. I believe that sun is a powerful as ever.
With new options like gigs drain for venusaur and volcarona as well as pain split for ninetales, sun can really pull its weight.
Another secret ingredient to a successful sun team is LANDORUS. Ohmygosh this thing is a beast. I'm not talking about the physical set. Hail before this OU breaking set:
Landorus @ Life Orb
Ability: Sheer Force
Nature: Modest
4 Def / 252 Sp.atk / 252 Spd
-Rock Polish
-Earth Power
-Psychic
-Hp Ice
This set has won me countless games and it is so anti meta yet so good. It can pull its weight against all weathers, and it's bulk an power and speed is great.
Against rain, STAB earth power 2hkoes everything and psychic maims Keldeo. Against sand, it's typing is great, and it kills everything with all its moves. Hp ice for dragons and gliscor and other landoruses... Earthpower for the rest. Against sun teams, it can definitely counter sweep stuff like venusaur, and earth power + psychic kills all those grass types like venusaur and amoonguss. EP kills fire types like Heatran as well
However, the best thing about this set is that it's unknown. No one sees a special set coming. I can set up all day while rotom will-o-wisps me. Then I 2hko with psychic. Same with amoonguss and slowbro and Heatran. This set is just so great.
I never meant "sun didn't get anything", but the new additions are a lot less substantial. Everything got "more powerful than ever". Giga Drain Volcarona and Venasaur is no way as good or signifigant as giving
Garchomp and Excadrill back to Sand. Rain upped the power ante with Keldeo, Tornadus-t, and Thunderus-t (and you are willing to give normal Thunderus on top of that!). Reintroducing those suspects back is going to make it a two way race between rain and sand. There is a reason when you had Garchomp, Excadrill, and Thunderus around you had Politoed and Ttar sitting
up there while lowly Ninetales sat 6%. She still isn't used as much as her the other weather inducers, but ever since those were banned she has had a healthy climb to 8%. Now that was with garchomp and excadrill while rain only had thunderus to compete but with the addition of the new tornadus, new thunderus, and Keldeo (more powerhouses to compete) I'm sure Politoed would sit right up there with Ttar.
Landorus isn't "tied" to sun as much as the other guys are. But if you insist, physical Rock Polish Landorus could accomplish many of the same things the special set posted for sun teams before Sheer Force got released. EQ gets that same 2HKO on Keldeo, he kills Gliscor and Dragons with HP Ice, still gives trouble to Sand teams, kills Venasaur with SR, etc. The only things you can't do is OHKO Amoonguss (who isn't much of a problem for sun), get the no-miss 2HKO on Rotom-W, and have that no-recoil life orb (always nice). The point is Landorus didn't add
that much to Sun teams at all as much as you say, physical Rock Polish Landorus accomplished pretty much everything you said. Also who the hell will-o-wisps landorus with rotom-w if they outright kill with hydro pump?
Basically all of these new pokes, both introduced and brought back down, make sure sun doesn't get as much of a chance.