I realized each level in All-Star mode is more or less equivalent to a generation:
Level 1 - Arcade games (Mr. Game & Watch, Pac-Man, Mario, Donkey Kong, Luigi, Little Mac)
Level 2 - NES first half (R.O.B., Duck Hunt Duo, Peach, Bowser, Link, Zelda, Samus)
Level 3 - NES second half + SNES launch (Pit, Palutena, Mega Man, Marth, Dr. Mario, Yoshi, Captain Falcon)
Level 4 - SNES first half + GB first half (Sonic, Kirby, King Dedede, Wario, Fox, Falco, Meta Knight)
Level 5 - SNES second half + GB second half + N64 (Ness, Diddy Kong, Pikachu, Charizard, Jigglypuff, Sheik, Ganondorf)
Level 6 - GameCube (Villager, Olimar, Bowser Jr., Toon Link, Zero Suit Samus, Ike, Lucario)
Level 7 - Wii era and beyond (Rosalina & Luma, Wii Fit Trainer, Shulk, Dark Pit, Robin, Lucina, Greninja)