Standards like these may be proposed by a single entity, but they're not controlled by it.
The problem with amp4email isn't that it makes everyone part of Google (though I'm willing to bet it'll ultimately imply all MUAs will end up having to embed Chrome engine). The problem is with Google using its near-monopoly position to push a "standard" that makes e-mail serve its users less, and serve companies seeking to exploit those users more.
OTOH it's like a standard that you can build upon if it's foundational communication infrastructure (channels, touch points).
This means that stability on lower levels facilitates competition on higher levels. As long as nobody is excluded it's not problematic. It shouldn't be allowed to scrap services users depend on though, this would be a good organic regulator.