I think your analysis is US-centric. I don't think non-shale oil has peaked yet globally.

What you say about the economics getting worse and lower EROI may be true. It certainly seems like common sense. There are some counter-examples though.

The inflation adjusted cost of extracting oil from the oil sands in Alberta, Canada has actually decreased over time, not increased.

But generally I'd expect increasing cost of extraction to be the norm.