So the answer would appear to be no. You can use mediaManager.getFileURL(), though the documentation doesn’t exactly tell you that; it says you have to use it in conjunction with the return values of other mediaManager functions, but you don’t - there are other sources of these URLs, not least File/Document collection types.
Now I’d like to know why getFileInfo() returns parentFolderId. Is there actually any way to use that? I’d love to be able to determine programatically where in our dumpster fire of a directory structure a file resides, but how to achieve this was not obvious after a cursory reading of the documentation. In fact I couldn’t see any use for this value at all.