Removing disembowel will simply make triple melee the de facto meta, it's not just disembowel making double ranged good, but also the good amount of utility that exist in the ranged role.
If the goal of removing disembowel is to make casters a good option, then the role of casters must become better either in terms of pure dmg or utility itself. The problem of casters lies that their dmg has no sinergy and it is linked to healers which UNLIKE tanks do not dps 100% of time to do their job.
This makes physical buffs stronger than magical ones by a lot and when you consider that magical buffs are extremely rare it makes the casters much more worse.
Removing piercing in short it's not a good solution to this problem especially when the triple melee is creeping closer and closer to usurp the double ranged spot