Don't try to fight over grammar, please. It's pathetic.
Unholy DKs and Rets never topped any meters. Rets were only high on Molten because of multiple old bugs. The highest DPSers of WotLK on retail (seeing that you're talking about retail, otherwise you wouldn't mention UDKs on Warmane) are Fury Warriors and TTW Mages, followed by Combat Rogues. That's not made up nonsense, that's
statistics. Nothing on WotLK beats an ArP-capped Smourne + Gloren Fury Warrior in a tank and spank fight. If it does, then the warrior is bad - really simple.
Then also - Ret skillcap is quite low for PvE where you just have to mash your keyboard prioritizing Judgement>DS>CS>etc. It took me around half an hour bashing a dummy to learn a Ret's priority as if I've known it my whole life. The rune system of DKs by default means that they have rotations. Rotations can be learned. And that's the end of their skill cap. Pretty much every class has its own rotation/priority system and once you learn and can apply it effortlessly in raids, it means you've reached the point of mastery with the spec. Try feral druids and enhancement shamans in PvE and then we'll talk about high skill cap.
Also, what you're talking about is individual skill with each class, as opposed to what we're talking about, which is what each class can do. You see the difference? We're talking about max numbers, you're talking how "it depends on the player". We're talking about best performance here, you're talking how Rets top DPS meters. Yes, I've topped many meters with Rets. Does that mean that Rets are WotLK's top DPS class? Hell, no. It just means every single one from the rest either sucked or was undergeared. In most cases it's the first. I dare say around 60-70% of the people who play this game are below average in terms of skill, but again this is not the point and we've gone way off-topic now.