Before this started they had approx 280,000 ground troops. NATO estimates that 40,000 of those have already been neutralised (KIA, Injured or Captured). Then there's desertions. So without the desertions that's a huge chunk of Russia's front line capability already gone, especially when you take into account the ratio of 3 or 4 to 1 troops required in the supply lines to keep the front line troops supplied
There are also reports that high level Belarusian military have been in contact with Ukraine to say if they are ordered across the border, they will surrender (could easily be propaganda I know)
Putin is already calling in extra troops from all over Russia, which will leave him exposed and weakened in other areas of conflict (like Georgia for example)
I don't see where the massive influx of troops required to "Win" this can possibly come from