Females are just harder to hit because they're smaller characters, but they have the same, if not more damage than other characters. They're just as fast, have the same health etc.
obviously I'll not defend mkx ass balance
but there's this kind of 'issues' even in other fighting games
matchup specific combos and juggles exists even in street fighter and have consequences in a few matchups too (my knowledge stops at 4 don't know about V) and they're not limited only to females. even some normals could hit some smaller characters while completely whiffing on bigger ones
ofc their vision is a little more deep than mkx's but still, such kind of variety isn't new to fighting games