I know I'm new here, but I thought I'd share some thoughts on the Crobat issue.
Of the Pokemon that are capable of switching into Crobat's Brave Bird effectively, I know of only two that can deal significant damage to the annoying prick before U-turn hits: Cloyster and Piloswine. Without priority moves (of which, only STAB Ice Shard and Extreme speed prove useful against the bat), Crobat is guaranteed to get away without taking damage.
The problem with this however, is that in order to guarantee 2hko on a 252 hp/0 defense Crobat with Ice Shard you must invest 252 EVs into Attack, a +attack nature, and hold a Life Orb for Cloyster or 216 Attack, +attack nature, and Life Orb on Piloswine.
Granted, Cloyster takes less than 100 damage from Brave Bird itself, but it also is weak to stealth rock, gets destroyed by Shaymin (despite being able to hit it with an ice shard), and is rendered significantly weaker at doing it's task of laying down spikes. Piloswine on the other hand eats 150 damage from min attack Crobat and doesn't really serve the same niche that it's evolution does due to lack of permanent Sandstream or Hail in UU.
Cloyster should be able to scare off lead Crobat well enough that it can get down at least one layer of spikes and explode on the vast majority of things that switch into it, but you still haven't effectively dealt with the bat or gotten your Stealth Rocks down in the first place. Piloswine however lacks the ability to explode, but can set up Stealth Rock, and might be considerable just for that reason.
Regardless, I think Crobat needs to be examined. No, it doesn't "Wall" everything in the tier. However, due to U-turn, Roost, and Taunt, it cannot be stalled out, taken down by brute force, or set-up on. Combine that with Quad resist to fighting, grass, and bug, immunity to ground, and all around sturdiness it simply lacks an effective form of removal prior to being the last pokemon standing. If you can tackle the other 5 members, then Crobat is fine; however, by simultaneously blocking the vast majority of pure offense, almost completely destroying stall, and setting up stall all at the same time it proves to be the most versatile pokemon in the tier while using only one moveset.