The mortar needs to be like what Mirage is doing in his mod. So big ups to Mirage for that one.
My way to fix the stuart is to buff its MGs. In real life that little tank could have like 5 or something MGs firing at once. Nerf the main gun to AEC levels and replace stun shot with a smoke canister like the shermans. This would give it some utility that requires micro to either attack or escape.
Rifles ain't as op as you make them out to be, sure they be good, but not gamebreaking unless they have double m1919, which is an atrocity. Double bars are okay. The problem lies more in the 4 man squads and their bunching. I made a post a while back where I suggested to have a sergeant upgrade with an MP40. This 5th man would be attainable through individual squad upgrades for a munition cost after BPH 2. He would not offer much in terms of medium and long range firepower, but would help survivability and short range capabilities. Of course this would warrent something for conscripts as well, but if you buff vanilla inf to be more on par with western front armies, then the whole balancing proces will be easier.
https://www.coh2.org/topic/51459/are-grenadiers-worth-their-30-mp-reinforce-cost/page/4#post_id517066
The .50cal needs to be a 5 man squad, it dies way faster due to more precise axis infantry, a flanked .50cal is a dead one, where a MG42/34 actually have a better chances of surviving. Anyhow that''s my oppinion on the .50cal.
Now things that really needs to be fixed in IMO are: forward retreat points, ambient building spawn, Mortar pits(needs to be replaced by a mobile mortar squad) and all the god damn call in meta XD but that's their own topic entirely!