I think paleographers think of the text as an abstract object and manuscripts as approximations of it. E.g. you might have a couple hundred manuscripts (and other things like printings, etc) of Aristotle’s Physics, but the text is what you get after you identify and try to correct scribal errors.
whereas I think in common usage text is anything written and manuscript is a subset of document.
Although manuscript in pre-computer days generally meant something handwritten, nowadays I guess you can turn in a manuscript that was written on the computer so not exactly the same.