To be fair by Smash 4 it really felt like they were scraping the bottom of the barrel for Nintendo owned characters imo.
At this point pretty much every relevant Nintendo character has been in the game.
I really disagree with this take. Smash 4's first party newcomers didn't feel like scraping the bottom of the barrel at all. Out of the first party additions, we had:
Villager - the face of one of the single biggest Nintendo franchises which, at that point, only had a stage.
Wii Fit Trainer - a representative of one of Nintendo's best selling properties. An unorthodox pick in and of herself, but the surprise factor was also a key reason for her inclusion.
Rosalina and Luma - a dark horse fan favorite from Nintendo's flagship franchise. Also gave Smash its first and so far only Puppet Fighter.
Little Mac - a massive fan request from an important and historic Nintendo franchise that got a successful revival three years prior to the project plan finalization.
Greninja - the Obligatory New Pokémon. We would've gotten Greninja no matter how shallow or deep the barrel was, but even still, Greninja turned out to be a good call due to its high popularity.
Palutena - a massive fan request from a successful series revival. Palutena's Mirror is literally what Kid Icarus is titled in Japan.
Robin - one of the main characters from, at the time, the single most successful Fire Emblem game, and the one that kept the franchise from literally dying.
Shulk - the main protagonist from a then-new Nintendo IP, and also a popular fan request.
Bowser Jr. - a popular fan request from Nintendo's flagship franchise. Also brings along the Koopalings, popular characters who originated in one of the most beloved Mario games of all time.
Duck Hunt - the token retro surprise character, who just so happens to hail from one of the best selling NES games due to Duck Hunt being packaged with Super Mario Bros. in the US.
Mii Fighters - Miis are some of Nintendo's most iconic and emblematic characters, especially during the Wii era. Wii Sports and the Mii Maker were cultural phenomenons that even inspired copycats with the Xbox Avatars.
Lucina and Dark Pit - last minute bonus clones who were, themselves, popular characters among their game's fanbases.
Corrin - main character of a recently released/then-upcoming title. Picked mostly because of timing and corporate synergy.
With the exceptions of Wii Fit Trainer (who was purposely picked as a surprise), and Greninja/Corrin (who were picked to tie in with recent releases, but in Greninja's case ended up being super popular anyway), I really don't see how Smash 4's first party roster could be considered bottom of the barrel by any stretch.