fly.io employee here, it's basically an adaptor from the Kubernetes world of YAML to the fly.io world of Machines. How could we have framed it better so that it was more clear?
A more in-depth analysis of which parts of the Kubernetes spec are unsupported by this adaptor would be extremely useful in evaluating it's viability for any given use case.
If the article was summarized with a TL;DR or phrase along the lines you mentioned "it's basically an adaptor from the Kubernetes world of YAML to the fly.io world of Machines" that would have made it way easier to understand.
In my opinion, the concept is not trivial to grasp by oneself (meaning: is not trivial to drive into that conclusion even after reading the article). So, being explicit first, and guide the reader through that concept along the article would have made a big difference.