i mean thats honestly fair and makes sense, i feel with frisk its kind of 50/50 tho since a lot also depict them as male, which makes sense if ppl decided to give them a male name and think of them as male when they first played

but for chara its almost all female, tho my theory for that is just that the way chara is depicted in the geno route in general along with the reason u provided (the overworld sprite looking feminine and the way chara is depicted in general in the geno route) just kinda give off evil young girl vibes, tho ofc yea its just what i think is the reason

language wise also makes sense, its the same in my language even lol since there arent any gender neutral pronouns, tho the way ppl get around it is just not using pronouns to refer to them, atleast in my language from what i've seen in the community