While it is true that Alph wasn't in Brawl, the point of Olimar having his personality stripped still stands. He was made to be a blank slate in brawl, even though he wasn't one in his games. I feel like the same could be done with ARMS, as Alph was stripped of his own personality, then placed onto a different character whose personality was gone.
They are dumbed down from time to time, but what I meant was how they act in their games. For example, Iggy Koopa is known to act all wacky and crazed, with many unnatural ways of acting and fighting to demonstrate that. Lemmy is also somewhat wacky, as well as dopey and constantly bouncing and balancing on a circus ball. in smash, neither of them use these traits and instead are made to act exactly like Bowser Jr., who usually just acts like a basic delinquent villain.
What I'm saying is, while yes it is possible, it is also much more likely than everyone seems to admit. Sakurai has very well proven in the past to do the thing you've said he likely isn't to do, multiple times over.
Are the chances that many of the ARMS characters being alts of Springman near 100%? No, but the likelihood of there being at least three other characters used as alts for Springman are quite high, much higher than many want to believe. The odds admittedly drop the more characters are added as alts, to the point where every palette is an alt, but still quite possible. More-so than many will admit. Just because it isn't a good representation of ARMS and the characters' personalities, doesn't mean its an unlikely scenario, as Sakurai has both added characters that many thought/think don't fit together and completely messed up or disregarded the representation of a character by giving them a totally made up and false personality (Olimar in SSE, Rosalina, etc) or just completely taken away personalities and voices, or even given them completely wrong voices! (K. Rool, Donkey and Diddy, Bowser, etc).