As a Rep I can say you almost all WZ I play Imps have at least 4 Sith Warriors, 2 Sorcerers and 1 or 2 assassins. BH and Imp.Agents are the strangest thing you can find playing vs Imps.
Reps usually have troopers KJ and Sages.. It's hard to find scoundrels, Guns and Shadows.
Fine, let me rephrase that, the core on most pub teams seem to consist of sages and commandos while on the imp teams it's usually made up by warriors or in some cases PT'es. The diversity was a reference to how the remaining 4 slots can go to different classes on the imp side. It's not uncommon that all spots on the pub teams, refering to pugs, are filled up by sages and commandos. Can't remember the last time I saw an imp team with 4 mercs. That probably never happened.
So yeah, it's always more fun to PvP on the imp side because you know that the chance that you'll end up with a really horrible class composition is much smaller than on the pub side. I've lost track of all the times I, as a pub, have queued just to leave (as in leave even before it has popped) 2 secs later under the presumption that it was going to suck anyway.
On another note, I don't think warriors are particulary OP. It's really annoying to go up against a team of 4 or more but in a mixed team they're perfectly balanced. Not to mention that there are far worse classes to go up against if theyre on the same team. Played a team with 5 operatives yesterday, that was no fun at all and I'd trade them for warriors, regardless of AC and spec, if I could.