code review is too late to give some of that feedback, and design/requirements documents dont have nearly the standardization of presentation and feedback tools for that to be useable.

Amazon does have those things, and has fine tuning on models based on those postmortems.

Noisy reviews are also a problem causer. the PR doesnt know what scale a chunk of code is running at, without having access to 20 more packages and other details.

You vastly underestimate the complexity of systems in a company like Amazon.

COEs and Operation Readiness Reviews are already the documents that you mention, but they are largely useless in preventing incidents.