Ukraine doesn't have to threaten Russia as a whole.
Ukraine can already reach quite deep into Russia. As Ukraine advances deeper into Russia, the deeper can they strike.
It's not just cannon fodder that Putin has to redistribute. For example, hw much air defence do you think Ukraine will find the further they advance from the frontline in the contested areas?
Russia has to move air defence closer to important infrastructure in places they didn't have to protect before. That air defence has to be taken from somewhere. My bets are not on Russia having a shitload of air defence units elsewhere that they can afford moving away from wherever they currently are.
Every unit of Russian air defence moved from Ukraine back home to Russia is making Ukraine closer to attack the Russian supply lines of the front lines. That's just one of all the things Putin is facing right now because of Ukraine advancing into Russia.
You're right, Ukraine doesn't have the luxury of time and men but they are surely hurting Russia badly with what they have. Even if the risk of Ukraine losing more than just the contested areas is big, they do not sell themselves cheaply.
Russia will pay for years and years for the "3-4 days to Kiev".
I checked the stats for the last 4 years here and it looks really strange. Statistics isn't my thing... But it looks like it's wise to be cautious and not to fully trust the numbers.
Around the beginning of last year there was a huge dip in the Windows market share that seemed to be correlating with a peek in "unknown". Windows then catched up in a somewhat erratic matter.
Mac OS also shows a weird behavior. Starts at 16%, up to 21% and the down to 14% between October and November...
It's not likely that a huge number of people decided to buy a Mac and then trash it I've month later. Samr but opposite goes for the windows stats.
I think it looks like there is an uncertainty of more than the total market share Linux is shown to have..
Not saying that Linux isn't increasing on desktop market share. Just saying that numbers seen to have quite a bit error margin and to be cautious if referring to these numbers.