That's a bizarre definition of "take advantage."

Then I assume you mean that one party is better off and the other party is worse off (taken advantage of). Sure, that can happen. But in the case of Amazon, the workers are better off or they wouldn't work there.

No, "taken advantage of" does not require one party to be made worse off. That is not the way the phrase is ordinarily used in the English language.

Sure it is. If I am taken advantage of, I am not better off for it.

You could be "better off", but still have been screwed out of being "even more better off". That's still being taken advantage of. Consider the legendary story about how Steve Jobs screwed the Woz.

Either definition works. You can take advantage of (exploit) someone at their expense, or your can take advantage of (leverage) their capabilities to mutual gain.

Frank took advantage of Amazon's 2-day shipping to do his last-minute Christmas shopping

Yes, but when someone says "Bob took advantage of Amanda" they likely do not meant Bob leveraged Amanda's capabilities to mutual gain.