“It was the team at Square Enix that suggested the hero from Dragon Quest XI as the main character and the heroes from past games of the series as variations.”
That’s a bigger deal than most people realize. If you look in any spinoff or crossover of the Dragon Quest series, you’ll notice no main entry protagonist is ever featured. That’s because they’re off-limits, period. Nobody gets to feature them, not Square Enix’s own Itadaki Street or Dragon Quest Heroes series!
Masahiro Sakurai has the chief honor of getting to feature not just one, but four of the Dragon Quest Heroes in his game, one of whom being the most influential of them all. He even got to request one of them specifically, the DQVIII Hero because he knew that was the most famous DQ Hero in the West.
For Super Smash Bros. to command such respect that a borderline-sacred cultural phenomenon will break one of its longstanding rules for it speaks the greatest of volumes for how far the series has come. Even moreso if Square Enix continues their practice of never featuring the main protagonists in other crossovers or cameo appearances.