There really isn't a perfect solution to this question. Syncing to a new Classic catalog, which I've tested, has a couple of issues:
The first issue is that Folders (in Lightroom) do not sync to Collections Sets in LrC, but all Albums in Lightroom should sync to Collections in LrC....so only the work of manually creating the Collection Sets in LrC should be required after the download in complete.
The second issue concerns that fact that not all metadata syncs between Lightroom and LrC. Specifically any keywords that you've added in Lightroom will not transfer to LrC, ditto for any Location data that may have been added in Lightroom (though at least any existing GPS coordinates DO sync, so the reverse address lookup feature in Classic would still be available to re-populate the location data fields). Face-tags also do not sync, so if you use facial recognition you'd need to redo that using LrC's own (different) engine.
Using Export Original + Settings that you mention also has issues, as NO album information is included in the exported files, so you'd have to recreate the entire Collection and Collection Set organisation from scratch. Keywords and Location Data could be included in the exported files, however. So depending on where you've focused your time organisationally in Lightroom (metadata versus albums), you should be able to decide which is the least worst option.
The third method would be to use the Adobe Downloader app, but I have to tell you that I think that has too many issues to make it viable as a migration strategy from Lightroom to LrC.....it's really designed to be used as a lifeboat for those users who are exiting the Adobe camp completely, and just want their image data out of the cloud. It needs work to make it into the better migration tool that you are looking for.
AdChoices