OTOH, it's the same question as whether presenting all the methods with the same name, or jumping to the one directly where you pressed M-.
Are you talking about jumping from a generic function call to a specific method invocation? I mean, from (foo ...) to a specific (defmethod foo ...)?
How would you know which method is the correct target for the jump?
my point was: how do you know that the user pressed M-. because he wanted to jump to the setf function? could be he wanted to actually jump to the reader function and the symbol was at hand in a setf expression.
but it would be a good feature that even though the xref buffer is shown, the setf variant could be activated by default.