I played through both the Great Patriotic War (Historical Difficulty) and the Russian Counteroffensive Campaign (Forgot the difficulty), and I noticed just how useless core infantry were in both campaigns.
In the Great Patriotic War, the early scenarios can mostly be beaten through OT-34 spam when maneuvered correctly and the auxiliary infantry are generally enough to break entrenched units in objectives. There isn’t much need for core infantry in the early scenarios and even less so in the later scenarios once two hex range KV-85s, IS-1s, Su-85s and T-44s become available. I find that the infantry are a bit too vulnerable to enemy heavy artillery to be of much use. Generally speaking, you can destroy most entrenched units through sheer volume of fire from tanks and anti tank guns, leaving very little room for infantry to be useful. The only time I found infantry to be helpful in this campaign was during the Berlin scenario, where a couple cheap cannon fodder infantry units were helpful to fill gaps in my overextended frontline, yet that was mostly because I was too lazy to come up with a coherent strategy, I’m sure it’s possible to beat it with a brilliant victory with just vehicles if you seriously tried. Anyways, I finished the campaign with a grand total of… 2 core infantry unit meant for combat (the rest were bridging engineers), and honestly, those two infantry units were deadweight 99% of the time.
For the Russian Counteroffensive Campaign, infantry is even more useless, none of the enemy is ever entrenched meaning you can just overrun through everything in the mid-late part of the campaign with hordes T44s. Seriously Russian Counteroffensive after maybe like the first 5 scenarios, just become ‘spam tanks and win’, very little strategy is needed for most of the scenarios (except for Sevastopol, that scenario was an absolute nightmare).
In general, I think the main problem with soviet infantry is 1. You have so many resources in Soviet campaigns that you can afford to replace them with tanks (unlike the German World Campaign where you do not have enough resources to make your whole army out of the most advanced tanks, allowing infantry to have some use). 2. The campaigns that feature them have features that counter infantry/ encourage tank use (long range arty for Great Patriotic War, and lack of entrenchment in Russian Counteroffensive). And I suppose this might be more of a personal nitpick, the lack of good transports like halftracks for the Soviets was definitely not helping.
Other than the infantry, the Soviet faction seems to not have a lot of incentive for combined arms, 2-hex range tanks and tank destroyers are all you need with perhaps a couple fighters for air cover and like 1 recon unit, you can honestly beat the campaigns without touching the rest of the catagories.