Crushing Blow blow needs to be more affective when more players join

For those who dont understand crushing blow is percent based so each time your crushing bow procs you remove 30% hp and as the monsters life reduces the crushing blow has less and less noticable affect because there life is reduced so the 30% on the last 30% of the monsters life wont chunk like it did on the 100% life at the start.
So my issue comes when a new player joins the game it will only still work on the premis of the orginal monsters health. So as that monster increases in life, armour and damage as more and more people join the crushing blow will still only do percent damage based on its orginal life before more players join your game… which is fine till you get to players 5, 6, 7 ,8 by then your crushing blow amount is reduced significantly now the 30% life from crushing blow when it procs is more like 10% on players 8 i feel like this reduced to much barbs are single target and they are not really good with clear speed when game is full with players.
Also armour has a big factor (if you dont have ignore target defence or your not fighting a elite or boss because ignore target defence wont apply to these targets) so now your dealing with a target that has huge hp more armour crushing blow takes less and less life because reduced affect against the monster, and now the life may have gone up 7 times combined with the armour increases also your attacks miss more and more becasue of the armour…
Crushing blow should be more affective when games have more players the barb