When it comes to Avatars in Smash, it makes sense that Robin is male by default since I feel like their story makes much more sense that way. In Awakening, Chrom and Sumia are heavily pushed which pretty much invalidates F!Robin's existence since her only reasonable S-Support is with Chrom, but M!Robin doesn't have that problem because he doesn't have the potential to be the father of a plot relevant character. As for Byleth, well, M!Byleth overall just has the better "stoic mercenary/Ashen Demon" look than F!Byleth does, at least in my opinion. But they're kind of a tricky case. Since there's multiple routes and multiple endings, there's really no canon to this unless IS actually establishes a specific route canon. Which they won't. They never do lol.
Corrin has commonly been established within the community that M!Corrin is canon to Birthright and F!Corrin is canon to Conquest. As for Revelations, it's up in the air. I personally haven't played the game so I'm in no position to debate it.
As for Kris, the game seems heavily biased towards as M!Kris as well. Not only does he appear on the game's boxart, but he also appears on the in-game title as well. M!Kris and Katarina are heavily pushed whereas F!Kris and Katarina get a shortened version of M!Kris and Katarina's A-Support. IIRC, so far he has two Cipher art, whereas F!Kris has none.
I'd argue a case of Mark being heavily male again, but his impact has little to no importance on FE7's story anyway.
Kiran is meant to literally be the player so there's no debate there either.
Then again, I'm heavily biased. Like, extremely biased. Whenever I play as an avatar or a customizable protagonist in general, I tend to play as a male because that's easier for me to self-insert upon, so I often like to see the male as canon. Though, sometimes I play the Pokemon games as the female protagonist because I feel like they were intended to be the canonical one (Dawn, Hilda, Serena, Gloria). But that's a different story.
Anyway, I still think Corrin should've definitely been default female though. Maybe future FE games will create an Avatar that they envisioned to be primarily female.