Conventional oil actually peaked around 2005–2006, but the shale oil revolution in the U.S. and technological advances have certainly postponed peak oil itself.

Here comes the kicker, though: we obviously extracted the easy-to-access resources first. While there may be counterexamples, looking at ore grades makes it clear that this is not particular to oil.

What happens next is that the economics of the wells are getting worse, which means we need a higher oil price for them to be viable. This also results in a lower energy return on energy invested (EROI), which reduces the surplus energy available to transform our environment. Consequently, this implies slower growth in the economy. Which I think is pretty obvious in the west and would explain the explosion of debt.

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.