But the IDE's ability to tell you depends on the language. IDE features for dynamic languages are worse because the static structure of the code is not available, so usually devolves into basic string matching. In the case of C#, the language and IDE support are developed together, and new features like async, linq etc are not considered done until the tooling (IDE, debugger etc.) supports them. It's unfair to dismiss the tooling for such languages when they were explicitly designed with them in mind.
I've been working with clojure professionally for over 4 years. The default navigation in emacs is non-existent as far as I can tell and only works at all once you've loaded the source into the REPL. Even that only works for resolving top-level vars and doesn't work for local bindings. Admittedly I tend to use cursive so this may have changed recently. But that still doesn't help you understand the argument/return types of functions etc.
maybe I don't expect as much as you do then.. I always felt a lot happier in a repl than in an IDE but I have to admit too that I didn't use IDEs a lot recently. (my last bits were scala and java graph moocs under eclipse and I was as angry as I used to be previously).
If you get a Request object, how do you know what is in it ? the IDE is telling you, not the language.