No, long before AWS, Amazon intentionally re-invested all of the excess revenue that would be reported as profit back into the business instead (expanding capex and opex).

I thought aws sprung out of investment in their own infrastructure. A happy accident of sorts, not some preplanned mammoth investment in building AWS from the ground up

Not at all.

AWS, or rather S3 was a pet project of one of the very early Amazon employees who wanted to do something fun. It wasn't really taken seriously or had deep strategy at first. Once it's started to gain traction, Bezos realized the enormous potential and full-steamed-ahead AWS.

Then it took many years for Amazon retail to actually start using AWS products in any meaningful way.

That's not how profits reporting works.

Yes, so 52% of Amazon's operating income came from AWS.

Which means, conversely, 48% came from Amazon retail and other services.

In other words, it's not true to say that AWS subsidizes the rest of Amazon, or that the rest of Amazon runs at a loss.