I don't think the Trinity is the problem, it's that they're designing all jobs to be the same in the name of absolute balance.

This is a game where multiple jobs share gear and you can play anything on one character. It's ok if some jobs are worse than others in some content and as they keep adding jobs, not every job is going to synergize well with every other. As long as any combination can pass content, I don't see why some can't be better than others, both in terms of personal and raid performance.

That said, most content seems to require 2 healers because they don't want people to wipe if the only healer goes KO and can't be resurrected, not because it actually requires 2. That sucks.