We don't use k8s and you don't have to either. This is for current and future users who absolutely want k8s. We are a compute provider after all and making it easy to host a great variety of apps is good for our users.
There are a substantial number of frankly ignorant people on HN who see K8S and run for the hills just because it is something they genuinely do not comprehend or were burned by an inappropriate deployment. The irony is that you arent switching to K8s, you are simply offering it as a compatibility layer, and still seeing flak. Case in point.
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.