But why we got Alph alt
No real reason to change his properties from Olimar since it's the Pikmin who do all the work. Dark Pit and Lucina are fighters in their own games and have slightly different properties to their counterparts, and Mario played differently in Melee. Makes sense to me why Alph's an alt and they aren't. If they were to retool Alph and change the Pikmin he uses to the new ones in Pikmin 3, that seems like it'd be more work than what went into Dark Pit, Lucina and Doctor Mario.