Yes, if you want a mature web framework that doesn't force you to use async then Rocket already exists, which is multithreaded and quite performant - and now allows you to use async if you want to.
Feather seems fundamentally single threaded and requires more boilerplate for something pretty simple. So I'm not sure the claim about developer experience holds up to scrutiny here either.
Feather seems fundamentally single threaded and requires more boilerplate for something pretty simple. So I'm not sure the claim about developer experience holds up to scrutiny here either.