In some senses, this can be seen as a good thing. Blizzard's intention is that players should "bring the player, not the class", so that there are no class/spec combinations that are so powerful that they simply must be taken on a raid. It also has the benefit of evening things up in PvP - classes that are more similar are easier to balance, which makes skill play a bigger role.
So this makes homogenisation a good thing, right? PvP is fairer, everybody gets to raid, all is good. Sadly, it's not that simple. Homogenisation has quite a few disadvantages too:
- Blandness: the more similar classes get, the more they resemble the same thing, but with different icons and animations. One of the reasons WOW has been so successful is the high level of re-playability - doing the same content as a frost mage used to feel like a completely different game to doing it as a destro-warlock. Nerf fear and give the destro-warlock a daze effect to compensate and you've got two classes that play in quite a similar way. This means that it's less fun to level up alts and play them in either raiding or PvP. If you're one of those players who has one main & perhaps a bank alt, that may not bother you, but for altoholics, that significantly reduces the appeal of the game. They'll get bored sooner and their subscriptions may vanish for long periods of time.
- All animals are equal, but some animals are more equal than others: giving the same buff to multiple classes may seem like a good thing, but it has consequences. Whereas before class A may have been preferred to class B because it brought a super-buff, we now have a situation where both bring the buff, so the choice is made based on other criteria, such as DPS. Now it will always be the case that one class will have better DPS than another, because perfect balance is impossible. If there's one thing we can be sure of in WOW, it's that the theorycrafters at sites like Elitist Jerks will find that better DPS class. This leaves us two possibilities: either class A brings more DPS and class B remains benched, or vice versa. Either way, the min/maxers will still take one and bench the other (and those who copy them will blindly follow), so there's no overall improvement from the situation before. Nobody's going to bring a frost mage to a raid when other classes provide the same buff, but with more DPS.
- Bring the player, not the class is a myth: top raiding guilds have always picked the best players. These are skilled people who can pretty easily re-spec to match the needs of the day. That hasn't changed as a result of homogenisation. There is still a "best" spec and only that will do in the top raiding guilds. The people who aren't interested in bleeding-edge raiding will still take non-optimal groups and deal with any problems by waiting to get better gear before they deal with particular encounters, just as before.
Resto-druid HOTs have been blanded into the ground because of PvP and their direct heals buffed. Now they're just different-shaped priests. I don't want that. Give me a variety of different encounters in the same instance, where HOTs are better for one and direct heals better for another. If that means I play my druid on some fights and my warlock alt on others (whilst Bob plays his rogue on some fights and his priest on others), so be it. That really is bringing the player not the class.