The fighter with precision attack is actually worse than the barbarian early and he scales without bonus action interference and maintains that +2 ASI lead for a decent portion of the career. Even longer for non-variant humans.TWF is already superior at damage dealing at tier 1 without feats but with this change those without heavy or ranged weapons can deal serious damage - for a price. Note though that 1st level PCs are very squishy and taking a -5 on your attack could prove a fatal mistake. I did consider putting the requirement of Proficiency Bonus +3 but that would mean ruling the feat out at level 4 and only fighters could get it at level 6 - others would have to wait until level 8..
Thus, IMO your proposed change is not balanced.