This criticism is spot on; it is exactly what I observed in late 2018, early 2019 as well. It's an awesome language, but there is basically a big case of 'vendor lock-in'. Certain compiler features are only available to the maintainers, nor is there any way to use alternative package sites. I don't want to know what would ever happen if the Elm developers decide to take https://package.elm-lang.org offline. That will…
These issues were obvious much earlier than that. I looked into Elm and was excited about it initially, in either late 2013 or early 2014. Then I looked into the history of some of the design decisions that baffled me (such as lack of type classes) and concluded the project was poorly conceived and led. The leadership didn't respect the opinions or capability of its end users.