The cold weather gear is not a significant component of game balance.
But this is a self-fulfilling prophecy - it's not a significant component of balance because it seldom gets called on.
I don't think it makes much difference that the cold resistance has no effect on summer maps IF blizzard maps are also in the rotation and the tournaments. All that would mean is that OKW then pay a presumably discounted increment for the fact that their ability is only relevant say 50% of the time. It would also play a part in the map veto process, as an Axis player might veto the summer maps precisely to take advantage of OKW's enhanced freedom of movement in blizzard conditions.
But when they never get to use it - and this is especially true in the tournament context - then it's difficult to see how Volksgrens are not overpriced.
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What I'd actually like to see, seeing as Relic are asking the question, is a tournament held exclusively on winter maps. I would be very intrigued to see if players made different decisions if they knew they would certainly be facing coldtech, and if the OKW ability is significant enough that it makes an actual difference to play. Other elements would also be brought to the fore; Ost might also be motivated to do more building of bunkers, and halftracks might be used more for troop transport rather than automatically being upgraded to carry a weapon.
I would find that interesting, although the general hostility to coldtech makes it unlikely.