Actually it's not. Group balance is a tricky thing that does not rely on a single job's utility/performance but on synergy. Trading multiple jobs to get the most of your group is the basis (look the MCH/3melees comp vs bard + caster(s) ). Of course, this is only optimization and does not matter one bit once you overgear a content, or in mechanics driven fights.
with that said
world first race is a special thing as you'll want to rush phases as fast as possible, ignore healing as much as possible to get more dps, etc... with world first in mind, you NEED to optimize the dps, and if that means ignoring X or Y job because they just can't push the numbers enough, then you'll ignore X or Y job. Once world first is done though, everything comes back to "what you are comfortable with", except for the idiots.