To be honest, I've always had the impression that a lot of people who play Smash don't really care for most of Nintendo's franchises, and only care about Smash. Not sure if that's really unpopular, or not, but it's always been the impression I got from things like the Nintendo Direct live chats, comments on YouTube, and even people on this website saying they weren't even considering getting a Switch until Smash Ultimate was announced.
Also, I'm not sure if this is unpopular, but I've always felt like a lot of the sword fighters in Smash receive hate due to how uninspired they tend to be. In-terms of visuals, most of the sword fighters in this game are just normal looking humans with crazy hair. The same could be said for a lot of other none sword using characters, but I think that they benefit from being more visually diverse. Also, lot of their moves also tend to be very similar/generic, which isn't helped by the fact that several sword fighters in the game use Marth as their template. Almost all of them also have counters, but I don't think that's a sword-fighter problem only. Ultimate's roster is so inflated that a lot of characters in the game have similar moves, and counters are one of the primary ones.
As much as I don't like Corrin, I think that she's probably the most interesting sword user (Robin to). He doesn't just use his sword, but also his dragon abilities. On top of that, his sword is chainsaw which the game utilizes on his f-smash. When you combine all of those elements I think that it really makes him standout.