I would like to hear more about battle experiences with Leafeon, Steelix and Drapion. Are any of them too powerful for UU? I haven't had much time to play/watch recently, but what little experience I've had with them leads me to believe all three are fine in UU.
I've been putting in some UU matches recently-- albeit I'm pretty inexperienced. I pretty much slapped together a team of the strongest UU sweepers with no walls (ie, I didn't use Steelix/Leafeon/Drapion) and saw how things could hold up. Team was: Luxray(semi-bulk/utility), Rapidash (mix), Scyther (BP), Absol(CB), Lapras, and Nidoking(Mixed).
I did see a LOT of these 3 pokemon, mostly because people are testing them I think. Reversely, I slapped these attackers together as a team to see how they could handle them.
I found Steelix's slowness and weaknesses were too easily exploitable. I mean it couldn't stop 5/6 of my team (scyther'd just BP out), and was constantly running away. Even luxray with Hidden Power 2 HKO'd it, and wasn't exactly afraid of earthquake (especially after intimidate). There wasn't a single match where steelix was able to switch in and wall me.
I even had one game where it came to 3 v. Absol, 1 full health absol v. 40% Steelix and 2 enemies Paralyzed by Luxray. Steelix fell to Absol's Night Slashes and allowed Absol to sweep the last two and get me the win. Problem isn't its defenses, it just can't do anything back. Well that's always been steelix's problem.
Drapion, while not weak, was certainly not over powering either from what I saw. Scyther would just run away with BP again, and it's not like it can set up SRs either. While it could earthquake, it's just not enough to damage to stop things like Nidoking, and not enough speed to stand up to things like Overheat Rapidash. Even Luxray (who I used as kind of a pseudo-gyara) could leave it severely hampered with T-Wave/Intimidate even after being weakened by previous opponents (Lux was my lead).
With Scyther, Rapidash and Nidoking, Leafeon was the least of my problems. From what I saw of Leafeon, it can't handle the same duties of a grass type as well as some others-- that is, handling water types. Leafeon did not like trying to switch into Lapras' Hydropump. That Sp.DEF is just too low.
Overall, from what I saw, the level of viable special attacking in UU is a lot higher than in OU because of lack of blissey and Hypno's exploitable weaknesses. As a result, the weak sp.DEF of these 3 makes them far from invincible.