That's a straw man. Nobody expects or asks for perfect balance. Of course there will always be some selection of jobs that are considered optimal on a given fight.

Ideally, the jobs are close enough that fight specifics vary that a little, or close enough that people get into debates about the value of certain features, i.e. mobility or unique defensive utilities, that dictate whether x job is better or y is better.

But even abandoning that ideal, just because balance can't be perfect, doesn't mean it shouldn't be good. "Don't let the perfect be the enemy of the good" is a common saying for a reason.

Sure, the definition of good can vary, but there's going to be a curve. It's not like every single player either doesn't care about balance at all, or would only accept perfect balance. Everyone has some point in between, where they'd say that the balance is pretty good. And you can definitely make things good enough to appease darn near all of them.

I'd venture to guess that the most common bar (aside from "so long as stuff can clear") is to want balance to be close enough that hardly anybody would think to exclude a job from PF, or to ask a group member to change jobs, or to ask themselves if they should.

If a player really likes job x and gets really good at it, that should be the best job for them to play. They should not be able to swap to a different job in similar gear, or worse gear, play it worse, and be a bigger benefit to their team in so doing.

And reaching that point does not take perfect balance. It just takes close-enough balance, gaps of maybe a percent or two, plus debatably-reasonable taxes.

Getting that close is very achievable. Maybe if you mix in design goals you can end up debating those, which is fair enough if we're told that's what's going on. But on a baseline do-your-job-SE level, potency bandaids to put production into the right +/- 1% range or so, is incredibly easy. It's trivial for us players to do just using fflogs, so if SE's internal tooling is as good as they claim, it should be equally easy for them.