D&D 5E (2014) Suggestions about making crusher, piercer, and slasher full feats

[TwoSix]

+Xd6 would be similar to +X/+X. remove +X for armors and we have new level of bounded accuracy.

+1dX or Xd6 is better if you want to mitigate usage of the SS/GWM mechanic. Flame tongue type weapons have anti-synergy with the -X/+X mechanic.