Back in April 2016 at the SEJ summit, a few months after the official launch of AMP pages in the SERP's (February), Google's Maile Ohye was asked whether webmasters should replace their Mobile and Responsive websites with AMP. We will discuss her response, and look at the comments from other Googler's since then.
According to TheSempost at the SEJ summit, Maile Ohyes rejection of that approach was an emphatic no, confirming that you should definitely not replace your mobile website with AMP.
Fast forward to the announcement by Google of Mobile-first Indexing, and the related discussions about how you should make sure all necessary content is visible on your mobile version, it would stand to reason that AMP would not be the most suitable way to display your standard mobile version, especially as AMP by its very nature are relatively streamlined.
When a question was asked on Twitter whether the AMP page has to have the same content as the "regular" page, implying that the user was using AMP as their mobile website version an interesting conversation developed.
@AlanBleiweiss "same" centerpiece at least. But forget the AMP part, they are just mobile friendly pages in our index.— Gary Illyes (@methode) November 13, 2016
The initial response implied that if you are using AMP page as your main mobile version then you should treat them as just a mobile version of the page.
Another ex-Googler then chimed in stating in no uncertain terms that "AMP is not a replacement for a mobile friendly website."
Repeat after me: AMP is not a replacement for a mobile friendly website.— Pedro Dias (@pedrodias) November 13, 2016
Following this up, another ex-Googler replied to Pedro's assertion saying that he is wrong. If all of your content fits within the restrictions laid down by AMP then it is not a bad option. John Mueller, webmaster trends analyst at Google, then chimed in confirming that it is possible, and that it is a very fast framework, giving a positive vibe to the idea:
The problem with most implementations is that they rely on limited default implementations, rather than a fully custom approach. For instance, many do not have navigation items, or even if they did, they may be significantly reduced. In some cases, commenting systems are not ported across, as well as other more advanced features.
In our case, we have implemented a more fully featured custom approach to our Accelerated Mobile Pages, but we have a fully responsive website as well. Ultimately, for most cases, this would be the best solution in our opinion.