Great Britain didn't stand a chance against Germany either.
Apple and oranges IMO. But, I get the David vs. Goliath storyline. Facts are as I see them that Ukraine has put up a great perhaps historic defense and the Russians have proven incapable of major operations. But, try as they might the Ukrainians still have conceded a significate portion of the East and South of the country. As the Time "opinion" article pointed out the Ukrainian economy is in ruin and a lot of their cities and infrastructure has been smashed. They have made strong stands but gains only when the Russian retreated or lack the impetus to sustain their gains.
Only time will tell but considering that Russia smashed the Ukrainian offenses in the Donbass back in 2013-14 (estimated 10,000 Ukrainian killed). I would find it extremely difficult to believe that they have the combat power to push the Russian army back in 2022.
IMO only a political change in Moscow or a complete collapse or mutiny by the Russian army would swing the establishment of one or more puppet states in the Donbass. Again, just my opinion.