The GEDCOM process does work, however, best used from a program such as GRAMPS.
A download from Ancestry and then upload to WT does not contain enough information to create a good profile. That is why most people suggest going it manually.
In my case, I combine information from Ancestry, FMP and FS, in GRAMPS and include a URL with each citation and some translations. The GEDCompare does a fair job of creating the profile, however I have put a lot of work into collecting the data/citations before this step. As many would agree, no one site has access to all the necessary information.
So, if Ancestry is your only source, I agree, do them one at a time using Ancestry as your tree model.