I can say how this worked for books. Used to be Amazon didn't enforce their pricing policy. So a bookseller could price their book's list price lower on a different site than on amazon. Amazon would discount to match, but pay the bookseller based on the list price.

It was effectively a way to get an excess commission out of amazon if you printed through their printing arm, Createspace/KDP. Not sure if this worked the same for non print on demand books but if you printed through createspace you could set a higher list price and get royalties that were about 100% of the actual sale price.

No idea if the same mechanic is in play with the FBA rules but it seems very plausible to me that the largest impact is has is closing exploits like this.

That doesn't mean it doesn't also entrench market position, raise a few prices at the margin etc but it's very easy to miss the potential for gaming rules, legally, unless you're actively in the system. If an incentive is there the market incentive will be to use it.