the Russian troops, most of which don't appear to be well trained.

Because they arent Russian troops they are freedom fighters from Luhansk and Donetsk. The Russians are providing air superiority, cruise missiles to take out hardened targets and special forces for unique missions and command and control. They are also providing logistics and supply.

If the Russians had 120k troops in Ukraine they would have rolled over the country in about the same time it took to roll Iraq.