Not to sound contrarian, but I honestly do think that at least giving themselves the option of cutting some "obvious" candidates to be able to focus on more mechanical uniqueness and fun concepts could lend to a better final product. I'm admittedly not 100% sure how much NASB2's moveset design and mechanics actually does take from NASB1, but a long-term problem with the Smash series as an example is that veterans are kind of seen as this "necessary" inclusion which results in massive amounts of development time being focused on them as opposed to new innovations and concepts (hence why the "reboot" concept for that series has drawn some popularity in online circles.)
Obviously Danny Phantom himself is a difficult cut to justify from a Nickelodeon-centred game, but if you're looking at a show like The Loud House which does ostensibly have a central protagonist but is pretty much equally defined by a prominent, reoccuring cast of side characters, then I don't think it's too bad a concession to go with a potentially more mechanically unique side character as opposed to having a roster that feels more bland across the board. There's a balance you've gotta strike with that sort of mindset, obviously - cutting Spongebob and replacing him with Mrs. Puff wouldn't work with this kind of justification - but I do think that a degree of openness would help a lot when considering this kind of thing.
tl;dr it shouldn't always be seen as a bad thing to pass up "obvious" candidates compared to more mechanically unique side characters, though on a case-by-case basis. it can be disappointing to miss out on some fan favourites coming back, i won't deny that, but the opportunity for new mechanics is a good one!