I wouldn't call the M1919 an offensive upgrade for riflemen already because that RM/M1919 has been nerfed some time ago and is more a defensive upgrade than anything else.
Giving the M3 to riflemen commander is a bit of an overlap with mechanized and I don't see much people using it on 2vs2 because it requires quite some micro to keep it in the right place to support correctly your moving infantry. To me the M3 is a new waste of slot for this commander.
i agree your opinion. it doesn't make sense. m3 half-track must be replaced to any other skill.