You know, as much as the Finland fanatics like to claim, the Winter/Continuation Wars weren't much of the war on the eastern front. Winter War: 70k Finnish Casualties vs ~350k Soviets. Continuation War: 225k Finnish vs ~900k Soviet.
Eastern Front: Axis ~5m vs Soviet 9m
Your casualty figures are off: some of them include all casualties, some of them only the deaths, and some of them are just plain wrong (looking at "350k Soviets" in particular here).
I have quite a bit of material on the Winter, Continuation and Lapland Wars and have done a good amount of research on those wars. I've made a post in the past where I listed the strengths and casualty figures for the Winter War according to the data I have, and I'll paste an updated version of that here. The figures involve only military personnel and certain types of vehicles. The casualties are in brackets.
Finnish Front 30.11.1939-13.3.1940
Soviet Union
1,500,000-2,000,000 men (200,000-300,000 KIA/DOW/MIA, excl. POW, 300,000-600,000 WIA, 5,000 POW, total: c. 500,000-900,000 men)
c. 6,541 tanks (3,179 were "lost" on the Karelian Isthmus alone, hundreds in other sectors, of which 2,268 to enemy action, the rest to breakdowns. Hundreds were however repaired or had parts salvaged from post-war)
c. 5,000 aircraft (1,000 lost, possibly more, c. 650-700 to enemy action)
Finland
c. 371,500 men (19,576 KIA, 3,273 MIA, of which c. 1,000 POW, 43,557 WIA, of which 1,437 DOW, total: 66,046 men)
38 tanks: 20 Renault FT-17s, used as static emplacements, many equipped only with an MG, 18 Vickers 6-tons towards the end of the war (22 lost: 16 FT-17s and 6 Vickers 6-tons).
c. 230 aircraft (64 lost, 47 to enemy action; 35 to enemy aircraft, 8 to AA)
The format is a bit messy but I hope that was comprehensible enough. I won't do strengths for the Continuation War in this post, so the casualties for that conflict should be easier to read:
Finnish Front 25.6.1941-19.9.1944
Soviet Union
c. 210,000 KIA/DOW/MIA, excluding POW
c. 550,000 WIA
64,000 POW
c. 2,792-3,000 aircraft (excluding non-combat losses)
c. 1,408 tanks, including assault guns and tank destroyers, of which several hundred were repaired or had parts salvaged from (excluding non-combat losses)
Total: c. 824,000 men
Note that the total losses of the Northern, Karelian and Leningrad Fronts, as well as those of the 7th and 14th Armies in 1941-45 were 688,145 dead or captured and 1,724,788 wounded, with 1945 making up 59,852 of the total casualties.
Finland
38,842 KIA
158,313 WIA, of which 13,260 DOW
6,912 MIA, of which 2,377-3,500 POW
215 aircraft to enemy action; 85 to enemy aircraft, 67 to AA, 23 destroyed at airfields, 18 from other enemy action, and 208 in accidents for a total of 423 aircraft
c. 50-60 tanks and assault guns
Total: 204,067 men
Regarding the Germans, looking at OKW figures the total irrecoverable losses on the Eastern Front seem to be in the ballpark of 2,500,000, with another c. 3,700,000 wounded & sick. I don't know if the WIA figure has the DOW correctly subtracted to avoid double counting in total casualties, though I doubt it is. It's also worth mentioning that minor battlefield wounds were often treated in the field and were not logged, and that this was probably rather universal across nations.
As for the Russians on the rest of the Eastern Front, Russian Military Archives have the card files from 1941-45 on over 14 million Red Army soldiers in dead alone, meaning their total casualties are likely at least around 30 million. Wikipedia, for all its inadequacies and inaccuracies, does have quite an interesting page on Soviet WW2 casualties. Here's a quote from there:
"David Glantz maintains that "the war with Nazi Germany cost the Soviet Union at least 29 million military casualties" (dead, wounded and sick) "The exact numbers can never be established, and some revisionists have attempted to put the number as high as 50 million""
Indeed the Finnish Front is dwarfed by the rest of the Eastern Front, even if you include the Winter War, which saw the Russians concentrate more tanks and aircraft against the Finns than what the Germans invaded Russia with in June 1941. Nonetheless whether you believe the high estimates or the low estimates, the amount of casualties in men and materiel the Finns caused the Russians in WW2 is massive, and should not be ignored in a game like HoI.