I mean that's a pretty interesting argument, but I think that giving Ness a skin that looks like Ninten is good enough. A skin would be pretty good, and plus his moveset could look more retro to pay homage to Ninten.
No, it isn't.
Them looking similar doesn't mean they have the same moveset.
In Mother 1, Ninten doesn't use any PSI attacks, while Ness does. Heck, Ness and Lucas have more similarities than Ninten does with Ness!
For a moveset, Ninten can use PK beam as his neutral b (a move he learns from Ana), a PSI controlled boomerang as his side b, 4th-D-Slip as his up b, and either PK Shield or telepathy as his down b. For a final smash, it can be either him, Ana, and Loid singing the 8 melodies, or using EVE.
Plus, this is the support thread for Ninten as a fighter.