I agree that there should be some variance on the LBs but it may also specialize certain classes for specific content and make them more sought after. The way to mitigate that is to make LB 1 and LB 2 somewhat homologous (like it is now) and then for LB 3 (in an 8 man) it branches out to class specific abilities so there are more tricks on the arsenal.

It's not an easy thing to design because afterall, if for example you come up with different DPS LBs only best one will always been called out.