Rosaluma: She was added for moveset potential, and it's creative and glorious.
Palutena: She's underestimated for being mediocre in Smash 4, but low she is (literally) godly.
PAC-MAN: Bamco helped make Smash. This is a thank you gift to them.
Robin: Somewhat creative FE rep with an annoying weapon degrading mechanic. Although Awakening certainly doesn't deserve 3 fighters, Robin is not the biggest offender.
Shulk: Because Xenoblade is cool, and should have a fighter regardless of what you think (this isn't directed toward any specific one).
Bowser Jr.: Ok, I get it. The clown car is dumb. But haing the Koopalings, as well as a creative moveset, is awesome.
Incineroar: Oh, I'm sorry? You're salty it wasn't someone else? Get over it. Incineroar is cool.