Yes Ukraine have undoubtedly lost a lot of soldiers, as well as civilians. But short of a general mobilisation of Russian men of fighting age, the pool of Ukrainians willing to fight is a lot bigger than the available Russians. And the motivation of Ukrainian fighters is much greater.
The US government have estimated that the Russian forces in Ukraine are down to 75% combat effectiveness. It seems as if over 15,000 Russian soldiers have been killed. Assuming a traditional wounded-to-killed ratio of 3-1, that would be 45,000 wounded - so, 60,000 wounded + killed out of an original force of 190K. Plus prisoners, plus deserters. And that's just in two months. I can't remember a major military power suffering anything close to these levels of losses in a comparable time period in a war of choice in recent history.
Who replaces these lost troops? Russia can't afford to put all its armed forces personnel into Ukraine - it has other things going on that it needs troops for, not least the defence of Russia itself. Belarus, theoretically in a military union with Russia, has declined to send troops to Ukraine. Other security partners in the Collective Security Treaty Organisation (Russia's pitiful attempt to replicate NATO) have backed off even further than Belarus.
So once the remaining available Russian forces are redeployed to Ukraine and then killed and wounded in their turn, where do the next wave of Russian troops come from? This year's conscripts, the teenagers (the ones too poor to have bribed their way out of conscription) with a few weeks' training? General mobilisation - an army of the poorly trained, poorly equipped and hugely pissed off?
And all this is before you get to the issue of how Russia can carry on arming its troops given the scale of equipment losses, the effects of sanctions and the time it take to build new tanks, helicopters, warships. Meanwhile, Ukraine is receiving seemingly limitless aid from the world's only military superpower.
Putin cannot win in Ukraine so he needs to decide which loss he can plausibly try to frame as a win.
Btw, the one pretty certain way for it to end badly would be if NATO stepped in properly.