Fighting games, especially ones like ARMS which are in their infancy, quite a lot of the time have interchangeable casts. The only reason Spring Man one ups everyone else is because he's the mascot NOT the protagonist. I really wish Sakurai or the localisation voice over guy didn't spread this false narrative that people were considering Spring Man the protagonist when it's obvious they weren't, they were considering him because he is quite clearly the mascot.
I fully disagree with the idea that Spring Man is the mascot. You mention in your comments the idea of large casts- particularly fighting games. He is the character that easily explains the game, a fully new concept (motion controlled first-person fighting game). He visually, and by name, tells parents to buy the game on the cover (which is incredibly important, we can discuss this more if you'd like); but it also explains the concept of the game.
The other characters, the ones with a bit more flavor, are not on the box. This is one of the few arguments as to why Spring Man is the 'mascot.' He is simply the Liu Kang of Mortal Kombat- the one who starts off to explain the game to a new audience. But, Liu Kang is not the mascot of MK- Scorpion is the mascot. Scorpion didnt really gain notoriety until the second game onwards, to the point that now he is used as emphasis on just about any MK media. This is how games based on character ensembles tend to work.
Animal Crossing didnt have a real mascot until Isabelle, many years after it's inception. Hell, the original Pokemon didnt use Pikachu as a mascot, the publishers put Charizard and Venasaur on the cover to sell games to parents... hell, it's the actual reason they switched to using Blastoise in America. Pikachu emerged over time just as- actual- mascots do of ensemble games.
I think given the noted popularity since her reveal, the voted on contest by ARMS patrons, the fact that she is in ARMS, Min Min will likely become the mascot. At the moment, there isn't one, just someone to explain the game.