Hmm....
well, back in the day (have not trained in years, sooooo I am beyond rusty)
My school did not spar with chest protectors, so no limit on that end.
Front kicks were very well used - but a back leg kick has more power, as you swing it around.
But it is usually also telegraphed from all the way back there.
I used front kicks a lot
Actually disabled my sparing partner - unintentionally - one time, catching her with my big toe right there in the soft spot on the throat, below the adams apple, between the two collar bones.
She choked and coughed for a minute, scaring the life out of me!
It's a distance game:Front leg, back leg, hands.
But the olympic style seems to be more like a round house kick match.
Not much finesse.
BTW, the face , while a good target in real life - especially the nose (ask how come I know), we do have to go to work in the morning, getting your face smashed in playing isn't a valid option for most.
Head gear was a valid target, face not.