Scenario 1 is an apparently complete Russian victory. Putin uses better tactics and a huge manpower advantage to achieve a breakthrough. The Russians take Kyiv and occupy virtually all of the country. Putin installs a puppet in Kyiv and holds a parade in Moscow. His casualties were enormous, but it was worth it, right?
The “victory” is illusory, because he doesn’t control the western border of the country, and he can’t go into Poland without causing a NATO response. He doesn’t have enough troops to effectively occupy Ukraine, even though hundreds of thousands of them are still there. Russia has the equivalent of an Iraq insurgency on its hands, with no end in sight, and no end to sanctions.
The fact of the matter is that Putin’s dream of controlling Ukraine died when his initial attack failed. The entire Ukrainian nation hates him now. It will never give up. As a result, the campaign wasn’t worth it, even under the best case scenario.