Fun fact. Every role can already do everything. You just need to customize for it, and it may not be ideal. It's especially easy to do this in non-savage content. Tanks can just DPS. DPS can be the tank. Healers can just DPS. Though some combinations are more or less advantageous than others. The mindset that tanks only tank, healers only heal, and DPS only DPS is short-sighted as hell. But when 99% of the playerbase only ever interacts with the most recent raids in standard party formats, they never put themselves in situations where roles break their standards.
Anyways, BLU being hybrid is fine. Maybe it won't be perfectly shoehorned into one role. That's fine. It can do everything - but not as well as everyone else. The differences get offset by how the rest of the party responds. BLU tank does more DPS than WAR, but needs special attention to survive? No problem. It just hurts the healers' ability to DPS, as they are having to throw out more than just regens to support the tank through boss autos. That DPS is made up by the BLU damage. Same deal if the BLU queues as healer. Maybe you just need to put more pressure on the other healer (you can already solo heal all Savage content, and some or all ultimate). And if the BLU is DPS? Well, maybe they being less DPS, but the DPS loss is offset by their ability to bring party utility.
When people see things only in terms of strict DPS numbers and shoehorn party roles, then yes, BLU is going to look like it can't raid. But if you actually look beyond that, it is perfectly fine as an imperfect raiding class.
Also, people may boot BLUs unnecessarily. But that's a people problem, not a design flaw. Same reason people think restricting content to i390+ will somehow get you better players. Maybe it will on average, but you're also keeping out some amazing players who just don't care about speedfarming gear.