This gets murky, but here’s how it works with FB Instant and AMP pages:
For FB Instant, the publisher introduces their ad tags into the FB platform. The FB platform also imports content from the publisher as you mentioned.
FB gets to expand their walled garden, and Intel from the data within it. That is of high value to FB. FB also gets to keep users in their platform this way.
With AMP, it is similar in a lot of ways. The pub makes amp ad tags and an amp template for content.
Google caches and hosts amp pages on their servers, and gives search carousel placement advantages to pub content that uses amp.
Google leverages data Intel from the pages they cache, which is of value since it applies for content on non amp pages that Google serves ads to. This becomes extremely valuable for Google.
For publishers, it’s a short term benefit of extending their reach into these platforms, but longer term it hurts because the ads that run on FB Instant and AMP pay less than those that run direct to the publisher domain.
FB and Google ultimately benefit from having the content cached from the publisher on their servers, and can use the content within their platforms for new features, etc.
Ads pay to the publisher in both instances.
In the case of Brave Payments, it would apply differently since the publishers are feeding content from their domain to Facebook and Google domains. I am not totally sure if you were asking in regard to whether the Brave Payments would carry over into the FB/AMP platforms, but wanted to mention in case that was what you were curious about.
I hope this helps clarify. I used to do a lot of work with pubs and FB/AMP, so this isn’t the official word from either platform, but it is based on the work performed last year with both systems (both platforms have documentation if you want to check into the latest info).