To be fair, it's a proxy war between NATO and Russia, and a lot of people did think that NATO was stronger militarily and economically because they didn't understand the difference between financial and industrial economy.

No, no, you see it's totally realistic to expect a highly industrialized country with vast domestic natural resources and a land border with a friendly manufacturing powerhouse and 20+ years of being forced into self-sufficiency by ridiculous NATO sanction temper-tantrums to wither in the face of the military might of a neighboring country with a land border and decades of being gutted by western vulture capitalists and which has had its military training informed by fascists high on their own propaganda supply. That's just common sense.

did anyone think that Ukraine could really stop a country with a population and economy of Russia?

Libs apparently. After decades of getting brains washed with narratives about "Asiatic zerg hordes" suicidally rushing into machine guns killzones and "economy the size of Italy" vs what they know well is entire economic power of NATO.

Ukraine is backed by the worst empire in the world with the most expensive military-industrial complex on the planet, and it's also not like there haven't been recent cases of the weaker side winning a war. I don't think that either of the possibilities should have been dismissed as completely improbable.