I don't think it's a lefty/right thing, I think it's a 4 seamer/2 seamer thang.
We've already seen that with Asher and Morgan when they returned with a 2 seamer.
The other key pitch is the changeup, because it throws off the timing on the fastballs.
One reason for patience with pitchers is that it often takes a year or so to master a change in grip or a new pitch, so you see them struggling, write them off, then viola, new pitch is mastered and suddenly instead of one good pitch and two so-so pitches, he's throwing two good pitches and his so-so pitche becomes merely a change of pace.