This is an excellent article, and it's something I've also covered (linked below).

I think that the Russians did expect/hope for a swift Blitzkrieg but they will have also had a plan B which involved slowly strangulating Ukraine by attrictional warfare, which is now being implemented.

I think the initial tactical successes enjoyed by Kyiv have lulled alot of people into a false sense of complacency regarding Russian capability and their willingness to drag the war into the winter.

https://medium.datadriveninvestor.com/putins-plan-b-comes-into-view-the-long-war-to-throttle-ukraine-2059e8155c22