if i am not mistaken, imenu only works for a single buffer, while org refile goto can go to any file configured for it.

at least, i /think/ imenu cannot be configured to, for example, find a shell function definition that is not in the current file.  for example, you might be in a script called myscript1, with a call like "myscript2 myfunc", where myscript2 is a script that defines myfunc and calls it when its first argument is it.  if htat made sense....  then again maybe xref and dumb-jump cannot either.  i have not investigated.