That artillery penalty is so that the player doesn't just flatten the map every time. Artillery really is the big decider a lot of the time, but it comes at a considerable cost. Also most infantry battalions, even in the Soviet army, don't have the luxury of calling in unlimited artillery barring special operations.
Be warned that the early SP-AT the Soviets get is very slow albeit potent. You won't see proper SP-AT until 1943 at the earliest, and even then the Germans have the edge for a long while. I would at least allow yourself a pair of T-35's or T-28's that you can upgrade into a pair of KV-1's later on. That's a pretty fair allotment of heavy armor considering the size of your force and is far from invincible. Their slow speed also means that when you commit them, they are pretty much stuck and can't rapidly redeploy across the map to help another sector.
Makes for a more interesting operational challenge
Re: Soviet infantry bt vs. infantry/tanks
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