If Russia is still in the war by round 10 with roughly the same income it had at the beginning, I don't see how the Central Powers could realistically win. Giving Russian infantry weaker offensive power doesn't seem punishing enough to me. It would also limit Russia's strategic options. Historically, they had to launch major offensives due to political pressure from their allies.
I think Russia's role of "destroying as many Central Powers units as possible before its eventual collapse" sounds much more interesting than simply spamming infantry and waiting.
By 1917, Russia was struggling just to keep its troops on the front line, let alone mobilize new armies. I even think its income should be close to 0 by round 10 (August 1917), even if it hasn't lost a single territory. With a -2 income modifier that increases by 2 each round, Russia would be at -20 IPC by round 10, leaving it almost bankrupt.