On the topic as mainly 4v4 soviet player: The only soviet units, which can be marked as weak due to stats (in comparison with other units of comparable role on the field)- T-34 with 76-mm F-34 gun, because other core tech mediums quite good even in extra late game, and probably partisans with PPSh-41, just because other infiltration AI units doing their job much better. I am not sure about partisans, because haven't played them much after september patch.
I don't know how KV-2 or Penals can be in the list of weak units. There is some units with questionable role on the field, like overpriced soviet paratroopers or assault guards (because coming only with M5), but even them are really good if used in proper way.
Relic Entertainment
