I don't get the idea that positionals prevent you playing solo.
I solo'd most of ARR as NIN and I have to say without positionals that would have been some boring stuff.
You don't need a tank to use positionals.
You time your attacks as the enemy is in animation lock, or you can stun them, or with enough practice, move to the rear/flank at the exact moment you need to, and if you're quick enough you can get it off before the mob rotates.