As far as I can tell, every other ult gets cancelled from a stun. Moira, Roadhog, even Tracer’s ults get cancelled if they are stunned while executing it. Why not Genji?
Genji’s ult is extremely powerful, and he is very mobile during it. There should be a punishment for allowing yourself to be stunned while using it.
EDIT: Please no longer base arguments on the fact that Genji’s ult is a “Transformation Ult.” My argument is basically about changing his ult to the “channeled ult” category but leaving his ability to use abilities, although I think it would be best to remove these categories in the first place.