Let's assume soviet purges are either different (couple of good officers are left alive, few bad ones get lead poisoning....) or there are competent people in charge of Winter war.
SU performs somewhat below what one could expect but not as bad as OTL. They achieve solid victory and are able to impsoe their conditions.
Results? Friendly Finland, Red army doesn't have that incompetent aura around them meaning Hitler will plan his war more carefully or differently. Maybe 2 year campaign from the start?
Thoughts?