Which Job, in your opinion, has the biggest identity issue?

[ty_taurus]

Well there's a bit more to it than that. SMN isn't the most played job in the game for player choice reasons.
Its entirely because of the arbitrary system in place that mandates you have one of each DPS type for an artificial damage boost in your party.
So SMN isn't competing with every other job, its competing with 2 other jobs.
RDM, the worst dps in the game at the moment, and BLM, a clunky yet difficult job thats pretty difficult to do easily on, let alone ask someone to flex onto.

SMN is quite literally the path of least resistance for a lot of players

You also get a free healer leveled out of it, a role a lot of people have no interest in, especially nowerdays.