AWS is certainly super profitable, if the ecommerce business was standalone, would it really be such a cash-gusher?

Amazon is successful because of the insanely broad set of investments they've made - many of them compound well in a way that supports their primary business. Amazon Music isn't successful, but it makes Kindle tablets more successful. This is in contrast to Google, which makes money on ads, and everything else is a side quest. Amazon has side quests, but also has many more initiatives that create a cohesive whole from the business side.

So while I understand how it looks from a financial perspective, I think that perspective is distorted in terms of what causes those outcomes. Many of the unprofitable aspects directly support the profitable ones. Not always, though.