The argument that uncapping merits will hurt uniqueness doesn't make sense to me, not only because, as Byrth has said, there's usually only one "right" way to merit but also because there's only so much time in a day. Even if you were to uncap merits people would still be distinct. I'm a BLU main, maybe Justin is a RDM main, Byrth is maybe a DNC main etc and we each have different secondary jobs and we only have so much time to devote to any job/jobs and getting gear for those jobs. Merits make no difference as far as uniqueness goes.
Edit: Also, there's a great amount of irony in the fact that SE is constantly increasing the caps on HP/MP, Attributes, Combat skills and Magic skills merits, which are the few merit categories that actually DO give decent to high functional diversity.