The Ukrainian army was 400k strong and quite experienced. They're badly out-teched, especially in the air warfare department, but they will make it up with morale - they're defending their motherland.

Russian army just does what it's been told. They're risking their lives to make a select few oligarchs a couple billion richer each. They don't want to be there.

If this doesn't end within a week, it'll take years. Putin knows this, hence the offers of unconditional surrender.