Just remove the heavy tag or the 'screw small characters' rule for heavy. Everyone who would get mad at that over ~my verisimilitude~ meaning halflings should such and fail at using weapons are already mad at the ASI changes, so there's no additional danger in making other improvements.
Both points of view--verisimilitude vs. player freedom--are valid, but WotC needs to pick one. The half-measures they are currently using are kludgy. Small and medium creatures are dramatically more similar than small and tiny creatures or medium and large creatures. No PC creatures can be large so Centaur PCs are medium, even though centaur monsters and horses are large. Goliaths are "little giants" as of MotM. What?I've started to think that small and medium will just get merged in 5.5e/6e, and become mechanically the same.
Which will be a shame.
If PC size doesn't matter, that's fine, D&D is full of abstractions. If it matters, make it matter.