That's a big part of it and Ukraine is more vulnerable because of much lower population and the threat of Putin sympathetic fascists taking power in the U.S., France, and Germany. However, there is more to it than that and that is the internal situation in Russia. Interest rates pushing 20 percent, massive inflation on many products including food, budgets spending absurd amounts on the war and cutting everything else, failure to maintain basic infrastructure such as elevators, continued dramatic success of Ukraine to hit strategic targets in Russia even while being irrationally restrained by the west. For cultural reasons, it's not reasonable to expect masses of regular Russian people to storm the Kremlin. HOWEVER, with each passing day as the war hits home in Russia more and more the chances of some kind of internal coup against Putin from insider oligarchs increases. Also such events as Ukraine finally destroying the Kerch bridge will add to the morale pressure for such a result. A new government won't be a liberal democracy, but it could potentially mean giving up the war and having Putin to blame, because they definitely need a target to blame. Not making specific predictions but a Ukraine win does not need to be a purely military one as that is indeed highly unlikely.