Except that doesn't put a physical link in the document. Why should I have to dig into the source code of the page just to find the link to the normal page?
You might want to use this web extension to make automatic AMP → HTML redirects:
https://github.com/da2x/amp2html
Or you could use this bookmarklet:
javascript:window.location=document.head.querySelector('link[rel="canonical"]').href