As a starter, if you're having a problem like that, you get beaten silly and then you have to wait five days to see how well you've corrected the problem. And if you haven't quite fixed it yet, then you get another beating and you've got to wait five more days.
Of course that gets to the heart of one of my bugaboos about starting pitcher callups. If the kid has to do that kind of basic work (e.g. learning to put a pitch where it needs to be), then he's got no business starting games in the majors. Every problem gets magnified when you're a starter. You can't hide. Sooner or later, whatever it is you're doing wrong will catch up to you.
I allow more leeway in the bullpen because the manager can yank that kid on a moment's notice if he doesn't like what he sees. It's certainly a good place to do your initial tinkering, to get a feel for what works against MLB hitters so that you don't get thrust into that punish-and-wait cycle. Even a dozen bullpen outings can tighten up a young pitcher's offerings so that when he takes the mound for a start he's better equipped for it.