The technical skills/teamwork was at a place where it was harder but fair and raids were fine because of more than just tuned raids, it could be said (easily) that heroic raids currently are harder now) and they are but BC was a good hard, more fair and less gimmicky. Did not have to have 10 stages of a fight, easier to learn but hard to master.
Maybe it's because people bitched too much, but I noticed a distinct lack of class-specific roles in raid fights in both Cata and Mists. I was a warlock who raided through Sunwell in TBC, and recall with fondness our guild's mage in PVP/stam gear tanking Krosh during the Maulgar encounter, and myself and our other warlock trading enslaves and banishes. I miss having to collect FR gear in order to tank Leotheras in SSC (although that was short-lived), myself and the other lock tanking Capernian during the KT fight (which was probably one of the most epic of all time), and tanking Illidan in Phase 4.
Raiding has seemed to boil down to extreme awareness checks (Alysrazor, Wind Lord, Iron Qon) or synchronization (soaking attacks, preventing adds from spawning, "get closer" or "get farther", etc.). I further feel that yes, while they homogenized the classes somewhat, there hasn't existed the need to use all of your class' abilities in some years. As a raiding warlock in TBC, I regularly used enslaves, banishes, searing pain, judicious uses of soul shatter, and other spells that haven't had a legitimate use since.
Granted, locks were succy-saccing shadowbolt spammers back then, but we had a lot of additional utility to employ to make up for that boring single target rotation. Farming shards also sucked, but it was what it was.
There just doesn't seem to be a need for separate classes anymore, aside from the obvious reasons of "so and so is more DPS, can offheal, or has a particular spell that helps us ignore mechanics."