Eliminating the top banner was something AMP announced they were going to do _months_ ago, just as soon as they could do so without negatively impacting performance: https://amphtml.wordpress.com/2018/01/09/improving-urls-for-...
And AMP having "the right to run their own arbitrary JS on YOUR site" is not something that can happen when you're not even being required to use AMP in the first place:
> we now feel ready to take the next step and work to support more instant-loading content not based on AMP technology
[emphasis mine]
Web packaging does still require including a named google js url, right? With little restrictions on what it’s able to do with the DOM.
Why, for example, is there no Google source saying that the AMP page header is going away? They have not yet specified if they will only allow a very specific implementation of web packaging that allows your site into the carousel and other top of page search result URLs.
Google could still be planning to keep the top banner, the left/right swipe to your competitor functionally for carousels, etc. That top banner, for example, has an [x] button that end users expect to dismiss the banner and stay on the page. Instead, it goes back to Google.
The negativity is because they aren’t being explicit as to what is actually being delivered. They are still retaining the right to run their own arbitrary JS on YOUR site, which could do almost anything they want.
TLDR: too soon to tell how genuine the message is, and Google isn’t working very hard to clear it up.