You'll find that's true of many many many other characters in Smash, many of which are aerial masters.
Simply put, you removed a lot of what I said, so you're no longer really responding to my specific content(basically you took it out of context). That, and you didn't really give an example of what you mean, so I can't honestly respond to your points. Could you please rewrite that so we can continue more accurately?
I don't think it matters to Nintendo and Sakurai if Sakurai thinks another character from 1 game can give something unique.
This. There is no such "one game = one character" rule to begin with. Nor is there a reason for one in itself. Even then, the fact a single game in a franchise can get multiple characters(especially when they're specific to it) shows how little of relevance this concept is. While it's not a perfect analogy, of course, when determining a character, "how many games they have" is one factor to think on, not the most important. Unfortunately, it's not really easy to think of a good example. In most cases, single game franchises often only one plausible character anyway. This is more of what's keeping them down. And sometimes Sakurai will combine multiple in-game characters into one(Duck Hunt is pretty much three characters in one as part of the moveet, after all. Duck, Dog, and Hunter, but also cameoing multiple characters too) as is. Overall? I don't see a good reason to deny another ARMS character. They may never come up due to ARMS getting no seeable new content in the future, but if he has an idea for a moveset that works, they would still be on the table anyway. They might be out prioritized by other characters, sure. That happens all the time. But again, these are more logical reasons then trying to administer a very arbitrary rule to begin with. That's not how business works in itself.
If a game gets tons of releases, it's relevant to business and the public eye. Thus, that alone can justify a second character. Seeing a unique option you want to add? Easy justification. That doesn't mean a single-game franchise is likely to get a character either, but they aren't going to be arbitrarily barred likewise.
