I agree very much on the lethality point, flanking does not feel strong enough, and it's mostly to do with the damage that the standard infantry weapons do.
I think the support weapons are too resilient on their own, if they get overrun they should really be in trouble, as is they can just run away most of the time, they don't even have to retreat.
Changing it will impact the overall balance though so I'm not sure it's that simple.
The cover issue is perhaps more of a map design thing, standing in green cover feels pretty strong to me, at least my guys can live a long time under fire there and even avoid getting supressed if they're all behind cover. There's just not as much green cover in Russia compared to France