auto potion isn’t the single best reaction skill in the game (that’d be blade grasp, and hamedo and counter aren’t slouches, and even weapon guard can make some of your guys unhittable with late game +30% evade swords) but if you don’t keep any potions in stock and force it to use hi or x potions it is very very good. mostly it’s like a de facto great mid game strategy for when you have to do a couple of otherwise extremely tough solo battles (the Gil economy is preventative before that anyway).
FFT isn’t that badly balanced so much as it’s like BG3 – a half-dozen classes have extremely extremely powerful synergies that aren’t really called out at all if you’re playing blind
monk and chemist have the largest utility skillsets (and some of the best reactions) for physical and non physical units respectively, ninja and regular old wizard have the best stats/passives, and lots of other jobs (as mentioned, samurai, thief, summoner, time mage, and to a lesser degree knight and lancer) are good dips to pick up 1 or 2 overpowered attacks or reactions