"Ayano appears to be dumber than (Shouta)"
I dunno... Shouta was pretty dumb, even for a 25 yo in a 10/11 yo body. Heck, even as a 25 yo, Shouta literally made a mess in his underwear virtually every chapter (and yes, we know from the first chapter that he does make a mess).
Ayano at least gets the excuse that she isn't an isekai character. And even when we combine both girls, we don't have a 'big O' every chapter either (though, of course, there are ways to be ecchi without going there...)