He's obviously not "crazy" (a term often used to excuse criminal behaviour); he justified his actions rationally. And he justified it using his own culture, which is notorious for normalising rape.

If his intent was, inferred via his own admission, to rape the kid, should he get a reduced sentence just because someone stopped him?

You can't have it both ways. If "intent matters" such that good intentions absolve bad actions, then bad intent needs to be punished as though the actual crime was committed.