Generated interfaces are an anti-pattern. Types force tight coupling between clients and servers. What if a third-party project written in a different language wants to communicate with your server using their own client? Types will make it more difficult for them to integrate because:

1. If they're using a dynamically typed language, this gives them extra work to typecast everything back and forth whenever they need to communicate with your system.

2. Even if they use types, maybe their type system is not compatible with yours and they need to do a lot of tedious extra work to typecast everything.