The question would have been better if it asked if Physic could have been changed back to Sustain for summoner.
That'd solve all the problems at once, wouldn't it? Physick on SMN is so weak as to be useless. Sustain was removed because of ability bloat. Replace SMN's Physick with Sustain at level 30 when the job is unlocked. Boom, SMN's useless heal is removed, replaced with very useful pet regen, and no ability bloat. (Sorry SCH, but at least the fairies default to self curing in a pinch.)