Look at the following sentence
Who did Ram see?
This can be paraphrased like this, isn't it?- Which x is such that Ram saw x
If so, what about the following echo question?
Ram saw who(m?)- can this be paraphrased in the above manner?

That generalization does not hold for some languages,including Malayalam a wh-in situ languages.This language has a different way to express echo questions. The language do differentiate the two

Does it differentiate them semantically as well as syntactically? I'm not sure what that would look like.

Imagine a language which has a question particle that mark interrogatives in addition to an in situ Wh-phrase.What reading would we get if we skip the question particle? Wouldn' t it sound like an echo question? It happens in  some (if not all)spoken varieties of  Malayalam,many spoken varieties in the language  use a particle (e(e)) attatched to the main verb, if this question particle is not pronounced the utterance get an echo-question (like) interpretation....... Not requesting for information,but seeking confirmation of an information- isnt that the property of  an echo-question?