That is true. Given Scrivener’s limited pdf functionality, and that imported pdfs increase the size of projects, depending on how one works and the kind of pdfs involved, there may be little advantage to importing.
In another thread about a month ago, I posted this, which might also be useful here.
When I want to include a pdf in a scriv project, I create a binder doc where I want it, give it the name of the pdf, then (from Windows Explorer) drag the pdf right into that document’s edit window, where a link is created to the pdf. When clicked it opens right up in my default pdf viewer. If the pdf is in a stable location, it should continue to work. And, as the pdf is updated, it should always open the most recent version, if it is saved with the same name and location.
I would add to that that the only thing useful I see in importing pdfs is that their contents are searchable inside Scrivener. But essentially the same thing can be done by simply copying the text from the pdf and pasting it as plain text (or even formatted rich text) into a regular Scrivener doc. Then, with a link to the pdf at the top of that doc, viewing the full thing is just a click away.
I’ve been using PDF-XChange Editor and am quite impressed with it. Even in evaluation mode, it still functions very well as a full featured viewer with saveable annotations.