I'm going to need your link as I couldn't find it going back in your post history (I don't doubt you did, I just couldn't find it). I just don't see many third party female options that stack up against the franchises we always discuss. DOOM, Crash Bandicoot, Tales, Tekken, Ninja Gaiden, Undertale, Devil May Cry, Ace Attorney, Soul Calibur would all be represented by male characters first and foremost. You might get a Coco Bandicoot alt at best out of those, and Undertale might just get away with a female rep. Then Resident Evil might get Jill as a choice. Stuff like Elder Scrolls would be need to be both male and female alts to actualize the character customization aspect of things and the same for a Monster Hunter. I just genuinely don't see a lot of good options as far as remaining big third parties go unfortunately.
As for ARMS, I don't know if we can confidently say it will get a sequel or if it will just join the Nintendo forgotten IP hall of fame. 1-2 Switch also sold 2 million units and it's certainly not getting a sequel any time soon. ARMS was very much a game that came out in the release window of the Switch and was the first, first party game to release since Zelda that wasn't a port of an older title. It had a motion gimmick and was trying to be the next Splatoon. It was an average, barebones game that managed to achieve those sales numbers by being the only thing to play at the time and Nintendo didn't support it for terribly long afterwards. It's the game I've seen people with the most buyers remorse over purchasing the title too. I think Nintendo just wanted something for year one of the Switch and threw the game out there to keep a sense of momentum going. I don't think it would sell as much if released today and I do doubt its future as a "franchise." And I certainly don't think it deserves to be anywhere near Smash yet.
Weren't the issues with MvC:I's roster primarily focused around the Marvel roster and not the Capcom roster? Like, yes, it had fewer characters overall, but looking at the Capcom roster I don't see many issues other than it sadly dropping some cool characters like Phoenix Wright and Amaterasu. I didn't keep up with the Infinite drama, but I remember hearing more grumblings about the Marvel line-up from afar.