I'm saying, the hypothetical flow from Google is:
1. Our Chrome detection relies on the User-Agent header.
2. But people can just lie in the User-Agent header.
3. Let's get rid of it and use something that's harder to lie about.
Closing any feature discrepancy isn't a goal here, as far as I can see. The whole point is to lie to the user that a feature discrepancy exists when it doesn't.
You can make the argument that Google is free to do their browser detection however they want (and therefore doesn't need to solve this problem by eliminating User-Agents), but this is still an obvious example of the User-Agent header causing problems for Google.
Many people assume Google, as an upper-level business decision, purposely makes products work better on Chrome in order to vendor-lock users to the browser. Maybe that's true; or maybe it's developers being lazy and using User-Agent detection. Removing their ability to do so might actually improve cross-browser compatibility of Google products.
So Google developers don't need to improve feature detection - that part is working fine already.