You are spot-on about your criticism of oligopolies as an explanation. But for your theory, you have to explain the absence of inflation from 2008-2019. It's not like government spending was sane during those years...
also, giving people money directly with stuff like unemployment and stimulus checks is extremely stimulative compared to say building a bridge.
massive supply shocks didnt help either. but they govt knew there was supply shocks and increased demand anyway. despite warnings by democratic economists. (we just found out yellen herself had misgivings about the 1.9T price tag)
