in the preludes u get feldwebel schulz, if u combine him with oleh dir and train them well they can easily get steamroller by 1942. thats 4 infantry killed per turn with that unit. should help a lot. other than that try 10.5 cm arty/towed rocket artillery that cost only 3 core slots and get more units on the field.
if u want more tipps i need more details on ur troubles and what u do.

What I've had success with:

Have three main forces: one around the airfield/Victory Hex to the West, one around the Victory Hex two hexes to the East, north of the road and one to attack North towards the airfield at the top of the map. A small fourth force can easily guard the Victory hex between your main two defensive concentrations.
Use your attacking force to sweep any units threatening from the North and secure that airfield, which will mostly eliminate any air threat. Then bring this attacking force down to relieve either or both of your main defensive forces in the East and West and eventually capture all the other victory hexes.

You should have some pretty OP heroes by this point, so lethal 21cm guns, vigilant tanks, the shulz overrun infantry, etc should all provide the resilience you need to let them mostly exhaust themselves attacking you

Excellent, that really helped. Thanks guys!