There's a good deal that I feel is lacking, but a big issue is the lack of continuity of documentation between Phoenix's component parts. If I want to build a CRUD app with Rail, Django, or Laravel, then I can get all the information I need from their docs. If I want to do the same in Phoenix, I'll have to jump between the docs for Phoenix, Ecto, Plug, and HEEx/Liveview.

Rails, while it has its equivalent of these modules, presents them in a cohesive manner and makes it clear the role they play in the greater context of the application. Phoenix doesn't make it nearly as clear and instead of being able to gradually learn these various concepts as they become relevant you have to take on the burden of them all before being able to even begin to be productive.