I don't think anyone has here has posted "no games = auto seller."
What I am suggesting is that ARMS, with it's particular circumstances, could see a boost in sales associated with being a big fish in a little pond - like you suggested.
In November, it may not stand out against the oft rumoured Smash. Or the bigger library of Nintendo ever green titles that will be one the market for holiday buyers.
Smash is still its own thing, and has button inputs which is still a little more "core" than the casuals are used to, as in, I can't play smash with friends like I can NintendoLand. ARMS breaks down that barrier with a very accessible control method. Besides that, Smash is about celebrating the history of video games, which is inherently for the more core audience, where as ARMS is an entirely brand new IP, which allows everyone to come in with no attachments and no prior knowledge other than publicly available videos and articles. ARMS isn't gonna be hurt by a XC2 or Mario Oddyssey release.
Personally hoping Smash is announced as a sequel like Splatoon 2, and it comes out Q1 of 2018, would give ARMS a little room to breath among the core, allowing them more time to focus on it and build its brand before Smash tries to take all the air out of the room, via headlines.