I'll not repeat what others have pretty much said already, but while I'm here-
Yo, Sebazy, Norrath turn-of-the-millienium-raiders represent!~ Let's go down Trak and maybe pick up a fungi tunic if it isn't camped.
I also agree that our rigid 2+2+4 structure helps limit things compared to WoW - I stopped not long after LK, too, but it was standard practice to only bring as many healers as you needed. You'd spend roughly all your time healing because if you had 8 people capable of healing the 25 man but it only needed 6 for that fight to be comfortable, 2 of them would go DPS or swap out. A 15-20% hit to raw, max healing output is easier to tinker with than a giant 50% slice. Coincidentally, it was always a rougher decision in our 10 man to try something with 2 healers or 3 healers. Bigger slices of the pie per person.
Nobody really has any level of real offhealing, either, like enhancement healing rain or even boomkin rejuvenations in frostmourne phase for HLK (had to do that in 10m, holy paladin wasn't mobile enough), so we fall towards superfluous healing until major mechanics happen that REALLY want you to have more than one healer - which leads to the natural conclusion of healers DPSing when not necessary to heal in order to push the most out of their job in a raid setting. Clemency perhaps, but it's not on the same level as the flexibility offered in some other games.
I haven't raided in WoW in a long time obviously, but can say with certainty back then, the 25m, 10m, and occasional 15m structures were set up to be way more flexible with primary role comps than what we've got here. Since we can't be as flexible we have no choice but to start maximizing what we're stuck with.
