For HC, an ability proc gives you 50% of your attack as "advantage". If you're against Know-How, raise it to 60%.
For Charm, a proc gives you 100% of your defense as "advantage".
For K-H, you get 10% of your Ego as "advantage".

If your stats are all equal (same for your Alpha), your defences (the first number) will be equal to half your damage. Realistically, you should have much more mainstat than other stats, so we're probably looking at something from 1/3 to 1/4 (or even lower) instead. Your final defences might be closer to 50%, but that won't matter until all 3 girls are on the field, by which point the battle is probably over anyway.

Your Ego is also probably at least 5 times higher than your damage, probably closer to 7-8x if you look at the first damage number (at least that's what I'm getting no matter what gear I have on).

This means that K-H ability is around 50% better than HC, and HC is 70-100% (or more) stronger than Charm.

Sure, technically you can trigger different specialties than your main stat by using different girls, but since for beta/omega *ONLY* (your) primary stat matters, there's no way that is a good idea.

The worst part is that this is extremely obvious just by looking at the numbers, and I'm sure devs have plenty of data on what common player stats look like. How the system got released in this state is beyond me.