I think the Classic Mode unlock chains should have been themed
Here's how they should have been arranged:
(in no particular order)
Mario: Bowser, Bowser Jr., Daisy, Dr. Mario, Luigi, Peach, Rosalina & Luma, Sonic
Donkey Kong: Diddy Kong, Ken, King K. Rool, Little Mac, Mr. Game & Watch, Pac-Man, Ryu, Snake
Samus: Bayonetta, Dark Samus, Inkling, Isabelle, Lucina, Palutena, Wii Fit Trainer, Zero Suit Samus
Link: Ganondorf, Marth, Pit, Sheik, Simon, Toon Link, Young Link, Zelda
Yoshi: Chrom, Cloud, Corrin, Ike, Richter, Robin, Roy, Wario
Kirby: Dark Pit, Duck Hunt, Ice Climbers, King Dedede, Lucas, Meta Knight, Ness, Villager
Fox: Captain Falcon, Falco, Mega Man, Olimar, R.O.B., Ridley, Shulk, Wolf
Pikachu: Greninja, Incineroar, Jigglypuff, Lucario, Mewtwo, Pichu, Pokémon Trainer
Mario's chain would consist of other characters in his series, and his former rival Sonic
DK would have the other characters in his series and numerous other characters that debuted in the 1980s on a non-NES/Famicom platform
Samus would have all the female characters not in Mario or Zelda
Link would have all the characters in his series, plus 3 "cool" characters that also debuted on the NES in America or Famicom in Japan
Yoshi would have Wario, the one remaining Mario sidearm character, plus characters would would likely see Yoshi as a beast that must be defeated
Kirby has the other characters in his series, plus other cute characters and Dark Pit (who is assigned to Kirby arbitrairily)
Fox has other characters from science fiction games
Pikachu would have all the other characters in his series
This makes more sense than just randomly assigning characters to unlock chains.