>I hope with you but the force asymmetry is large. But so far they have been doing much better than could have reasonably been expected.

It is not that large. I remember an estimate of some strategist that you need 5x more firepower to win a battle in urban environment (cannot find the link, sorry). Even if Russia sends 20-30% of its entire army and national guard to Ukraine, this would mean only a parity with highly motivated defenders. Russia certainly has better equipment and air support, but it may still take a lot of time and casualties will be high.