Without good medic: nobody gets healed effectively (or at all) so it’s up to assault to kill monster as fast as possible and support to keep people alive.
Without good support: the group has to be more careful in engaging evolved monsters, and medic has to pick up the slack
Without good assault: the game lasts FOREVER even with a mediocre monster… The support has to revert to dealing damage as much as possible.
Without good trapper: you will never have a lengthy fight if all the domes are missed or not thrown at all, assault needs to do as much damage in short periods of time as possible.
That’s my list in terms of how hard it is to win with just one of the hunters being bad. Medic is hardest to win without and bad trapper means your going to fight a stage 3