Can Google demoted rankings if the content on your AMP pages is not the same with the non-AMP pages? Yes, according to their official documentation:

“these pages will not be considered for Search features that require AMP, such as the Top Stories carousel with AMP. Additionally, we will notify the webmaster via Search console as a manual action message and give the publisher the opportunity to fix the issue before its AMP page can be served again” – source (Google)

Some tried to use AMP pages with minimal content as teaser pages. These teaser pages will then lead to content-rich pages (with different content than AMP pages). Google doesn’t like it, and will apply a manual penalty if caught.

I haven’t seen how this message read in Google Search Console yet, so please contact me if you receive one.