Yeah they pretty much homogenized all classes to do the same thing but with just slightly different means.

I'm not saying that vanilla was "perfect" because they could have done much more in terms of making the classes unique, but at least in vanilla there was a little bit of some sort of niche that each class served.

For example if you played a Hunter you were needed because no one else had access to Tranquil Shot and you absolutely needed that in order to dispel frenzies from bosses, and apart from that Hunters had a unique job of kiting in BWL as well.

Also Druids being the only class who could combat res, so you wanted that ability in your raid hence you always brought Druids.

They could have made encounters offer more things like that, for example design a boss fight so each class has a certain niche within it so you need to bring them. Maybe not a single boss fight, but throughout a raid instance between different bosses making it so at a certain boss a Priest for example had a specific job at hand which no other class could do, and at another boss a Mage had to do something.

And they definitely did do that on certain bosses, but they could have done it better I think. For example in MC / BWL you absolutely needed Hunters because they were the only class who had access to Tranquil Shot, and in BWL they had a unique job of kiting on a certain boss. But later into the game in Naxxramas you didn't really see Hunters do much at all other than DPS, so the utility part of their class was not used to the full extent and other classes did better DPS than them so you needed that utlity side of your class to be useful or you were just lackluster.

But with that said, in retail it's definitely way too homogenized. It's just every class doing the same thing.