Not true, you can validate AMP from localhost. The AMP.js packages comes bundled with it's own validator:

https://amp.dev/documentation/guides-and-tutorials/learn/val...

Even then it's quite a stretch to go from saying Google controls AMP to saying the validator has an online requirement. Also, as the other commenter said, Google, Bing, and Cloudflare are currently the certified CDNs to get the icon in search results.