Nice thinking. I think there should be 2 upgrades, 1 is the Anti-Tank upgrade(AT,TH) and one should be the Anti-Infantry Upgrade(Snipers,Mortars).
I think the teching is fine how it is. Either add ambush in cover, which for some reason I thought they had already, or change PTRD vs 22x armour. Possibly do both. Also help the mosin-nagant out against PE vehicles because then you could actually win in you sit in heavy cover etc. like riflemen. At the moment you may as well be shooting at a panzer.
OSTHEER IS DONE WHEN IT'S DONE!
ketten push? you mean using ONLY kettenrads?
Although changing the support rax to an AT and AI path wouldn't be a bad idea. The mortar and TH have no synergy, while the AT gun and TH are meant to work together.
It makes more sense to divide it up this way so you DON'T have access to both with one upgrade. If you want the synergy, get both upgrades. It's not like they're dear or anything.