Hi there,
We’ve done some digging here to do some clarifications.
The tracking previously was indeed not done by our addon, as it does not run unless the Automattic plugin is both installed and activated. Further, none of the recent changes to it or to our core plugin would/should change anything with regards to frontend tracking.
The actual AMP tracking being done was apparently by the AMPforWP plugin itself, and at least in our testing still seems to work.
If anyone is having issues with their tracking working, please contact our support via the MonsterInsights support form in the My Account area of our site and we’ll take a look to see if we can resolve those issues for you.
As mentioned earlier, while the number of installs of the official AMP plugin on .org is not that much larger (its about 2x) the number of people using it + MonsterInsights is significantly higher. We generally support only the official methods of things whereever possible since we do a lot of automated and manual testing before each release, and every new thing we add support for adds a lot to that workload, thus why we only generally support the main avenue. Additionally, the last time we looked into an integration for AMPforWP there simply was not the user crosssection to justify it and it was going to be extremely time consuming. If the AMPforWP guys want to contact us via our site, we can see if we can work something out.