This list doesn't really make a ton of sense. It looks like a list of ssb4/Ultimate picks, but it also has Melee and Brawl ones, but it also doesn't have
all of the newcomers from those games either.
Since the previous list considers everyone, I'll do that here with what I think is more accurate (though, I'm going to exclude alternate costumes here since they kinda don't count with this angle):
Additions to existing series:
(43)
New series additions:
**
(45)
*Not an actual character.
**Unless you consider the Miis as Super Smash Bros. characters, but that's inconsistent even officially.
These...aren't the numbers I was expecting to be honest. And there are a few more asterisks here that control who wins like whether or not you count the Mii Fighters separately since while they are three different characters, they are also the same..."avatar character" for lack of a better term. It also counts the Super Mario series's extended cast as separate series, and not everyone agrees with the logic. Even if you hold those assumptions though, the difference is still 44-42 in favor of existing series (because Donkey Kong and Yoshi were added alongside Mario and Luigi), which still isn't that big of a difference.
It's also worth noting that having a ton of characters from existing series should be relatively high since most people like more than one character from a series, and you can't add them all at once.
As a bit of a concession, the story might change a bit once you separate it from game to game, and I kind of expect it to do so, but when looking at the series as a whole, there isn't that big a discrepancy.