As someone that played alot of "flash" Games in the past, i think Block will be the "best" ability. Sure everything is based on luck, but how about this:
Your opponent is stronger then you, he need to hit you 3x, but you need to hit him 6x
If you block 3-4x then you can beat him. Heal is another factor, but even if you have an "Hardcore" opponent: even if he crit and you block, then the dmg is zero.
Im a "know how" character and even if we can heal and attack at the same time, if feels a bit worse. So even if both need 4 attacks to beat each other and every skill triggers every time:
1. Know how waste heal = Hardcore 3hp
2. Hardcore crit = Know how 2hp
3. Know how heals back to 3hp = Hardcore 2hp
4. Hardcore crit = Know how 1hp
5. Know how heals back to 2hp = Hardcore 1hp
6. Hardcore crit = Know how down
So even if you start, you nearly can not win(depens on how often the skills triggers, so luck involved)
and if Charm blocks the most time, then im not sure how good heal is. Maybe you can not "die" if charm do not enough dmg and you slowly heal up and hit sometimes trough block, but if charm hits always and you do not always heal, then maybe heal is not good at all.
I feel a bit offendet by that, because i actually don't want to change know how (i mean my gear is based on know how) but if this new update come and know how gets "ass kicked", then it's like we get forced to change and everyone else is fine...