I wouldn't say that questions about Party compositions are opinion based (at least for those RPGs I play) but they can be quite broad if not narrowed down to a specific problem you're facing.
Let's take WoW as an example (this applies to most (MMO)RPGs with party elements):
If you're asking a question like "What setup should we use to kill this WoW Raid boss?" without much further information it will most likely be closed since It shows no effort on your side and is quite broad.
If you however mention the exact problems you have with your group in that encounter the question becomes much more accurately answerable.
Note that the why is important here: why do you need a new group setup?
As a rule of thumb:
If you know why you need a new party (composition) we can help you. If you yourself don't know what you are struggling with we'd have to make a lot of assumptions in order to help and that's a close reason.