Which is ironic, because the German division size was about equal to a Russian corps IIRC.
If my memory is more or less correct ...
1. The pre-war Russian rifle division, insofar as TO&E, was roughly equivalent to its German counterpart.
2. Within a matter of month after the German onslaught, the Russians were forced to reorganize by truncating its pre-war TO&E (due to heavy losses, but also the vaunted Russian industrialization came up short in providing adequate numbers of support equipments for their divisions). The Russians even went further by creating rifle brigades and eliminating the corps level commands from their OB. (They had to, because they had shortage of trained officers and the pre-war organizations have turned out to be too much for their mostly inexperienced officers.)
3. By December of 1941, the Russians have lost an equivalent of her entire pre-war army. Quite usual for an 'average' rifle division to be equivalent to a 'full' German regiment. The 'smaller' Russian division was probably less of a big deal, because they created 500+ division equivalents throughout the war.
4. Only divisions assigned to major offensive operations were brought anywhere close to its 'full' strength. Such a division may have anywhere between 6000 - 7000 men, but divisions assigned to quieter sectors may have as little as 2000 men. Meanwhile, an 'average' rifle division did not have priority over replacements; a select few privileged units (e.g., tank/mech corps, guards divisions, and combat support formations) had priority over replacements.
5. The bulk of Russian combat power came from their numerous tank and artillery units, which were under the domain of higher commands (corps and above).
6. A typical wartime Russian rifle division was very 'lean' compared to her German counterpart. The former had a light artillery + an AT-gun batallions, but the latter had a mixed artillery regiment + an AT-gun batallions + assault gun company/batallion (if available). The former's regiments, each, had a light artillery battery + an AT-gun battery, while the latter an artillery batallion + an AT-gun battery.