It comes down to whether you want to maintain a bunch of auto generated files which will never be automatically updated. I would rather maintain only the lines of code I write not ones that were generated by some tool and then immediately became legacy.
I understand that generator is for education purpose. New comers might find it's cumbersome to get start if generators are absent. However, I think it should be just some guide docs. Generated context can mislead the concept of how to use the context itself. It's easy to quickly write a dirty API in phoenix, but practice guides lead to ceremony.
If you want a quick and dirty API, using Plug directly may be an option: https://gist.github.com/josevalim/fbfc669aa6087c5b79402b399d...