Yeah Autotrack is not equal to GTM. To give you some context, Heap came our with retroactive analysis first ( for example, if you forgot to track an event on an app, you can go back in time with retroactive analysis to see how much people were clicking). This was one of top requested feature requests for MP. Heap came to us with this USP + the Visual Editor,better UI. Finally, MP launched this feature( we are on MP) and is free of cost.
Moreover,Heap just raised series A @ 11 M. Interesting turf wars with MP and Heap. Will be good to how the landscape shapes up.
We should be enabling retroactive analysis by tomorrow. Will let you know if we face any issues.
If you want to learn more about GTM( I am learning too).
I would recommend this training ( i took the 301 GA and it was amazing).
Or you can study from GA's own course
or you can buy a book on GTM by Luna Metrics