The problem is that the Russian Revolution at this point seems to help the Allies about as much as, if not more than, the CP. The Revolution does NOT provide the CP with a capital they need to win, although they still need to commit significant resources to making the Revolution occur, which makes the motivation for causing the Revolution to reduce the size of the fronts a dubious ground at best.
Another issue is that the general interpretation so far is that the CP is in trouble.
If Russia is made stronger, the other Allies need to be weaker in some way.
It seems like the more units the CP send to Russia, the more Russia WANTS to trigger the revolution, and the less troops the CP send, which would mean they are trying to knock Russia out and win with Rome and Paris, the more Russia will want to resist and the more capable they will be.
Perhaps Russia does not compare accurately to the CP in terms of sheer numbers, but another thing to consider is that in quality of fighting units, the proportion might be pretty close to right.