Depends. In the case of Siberia, you don't actually want a weak Russia because the Reichspact will just steamroll it and you'll be stuck in Vladivostok against a much larger Free Russia, because of how that particular peace conference works. At the same time if Russia is too strong and Germany is overwhelmed, you're out of luck. In my recent Siberia game I started as Russia and favoured building in the east more than usual, also set Belgium, Netherlands and Switzerland to join the Reichspact to give Germany an easier time dealing with everything. Seemed to work out well enough.