Uh, Cloud airdodges closer to when Corrin starts his roll... Definitely wouldn't combo in that situation, and since less knockback = less hitstun it means it doesn't end quick enough to combo, assuming Corrin acted as fast as he could. Even if it was the end of the roll, invincibility wears off on F17. 5 of that's going to be jumpsquat, and another 5-11 is going to be wind-up. (Marth and Roy's Fairs, or Marth and Pit's Uairs, for comparison.) If his attack is fast then that's a whole 7 frame window to follow-up on, which is reasonable. If it's slow then you have just one frame to combo with, but do remember that buffering is a thing. It'd be ruined if Corrin needed to delay his aerial a frame to actually hit though, and he probably would if they fly that far. With the current amount of knockback and a slow Fair it'd be impossible to combo with, but with less knockback and thus less hitstun it would still be impossible. Even with a faster move it looks sketchy.
The numbers aren't really in favor of Utilt being a combo tool, although I'll admit any number of unaccountable factors would pretty much ruin my math.
To prevent Corrin from, oh say, camping offstage against Little Mac, it probably runs out after a short period of time.
Honestly any kind of camping with the move sounds like it'd be too potent a noob tactic for them to leave in. Might not let you jump out of it twice in a row, like with the mechanic on Ike's Aether that only lets him regrab the ledge with it three times before falling.