Rotom's not legendary though. It's like calling Porygon legendary. Except for the fact Rotom has extra forms. But they both can be obtained in-game AND can be bred with ditto.
Meanwhile Phione (although can also be bred for itself, I think?) has to be obtained through Manaphy (Event legendary only). That's probably their edge in choosing there.
Meanwhile Phione (although can also be bred for itself, I think?) has to be obtained through Manaphy (Event legendary only). That's probably their edge in choosing there.