I agree with Trihero.
All Russia needs is one inf and it can attack Arch with 1 inf and ALL its armor.
Russia won’t be using its armor to attack Ukr, Belo, or Kar so it is just sitting there doing nothing anyway. And on R3 that armor in Arch is still within reach of Ukr, Belo and Kar if need be.
Now I don’t attack Ukr on R1 and I’ll buy 3 inf, 3 arm so I’ll have 7 arm available on R2. I attack Wrus only and typically Germany will counter with 1 inf in Ukr, 1 in Belo, and 1 in Kar. That means 2-3 inf, 1 ftr to ukr, 2 inf, 1 ftr to belo, 2 inf, 1 rt to kar and 1 inf, 3-7 arm to arch.
I don’t see how this is overextension?
If you block Kar, you’re likely to see this on R2:
Kar: 2 inf (possibly 1 if you hit on def)
Belo: 1 inf
Ukr: 1 inf
Russia still has to commit an rt to one of those battles or ignore one (which is the same as leaving Kar empty).
Essentially it is a wash if the German armor in Arch hits on defense. Germany gains 2 ipc and kills 1 inf (3 ipc) on defense but losses the armor (5 ipc). 2+3-5=0
But 50% of the time the armor misses on def, so Russia essentially trades Inf for Arm. I’ll take that as Russia all day long.