I heard many of these arguments along the lines of "NATO is responsible for the war in Ukraine because they shouldn't expand" - like prof. John Mearsheimer's famous video.

The point is, these experts may understand geopolitics, but they don't understand people. These countries don't join NATO because the USA pushes them or because "NATO wants" to expand. They do it because they're afraid of an aggressive state with a history of offensive wars. They don't want to became Putin's vassals like Belarussians who recently tried to decide about themselves and met with violent terror. So yes, in the mind of Putin it's the fault of NATO, but it is a very sick point of view.