There are lots and lots and lots of profiles with no source and no dates. I was reminded of the extent of the problem as I reviewed the site looking for profiles of people who have US Counties named after them.
I don't know if they all come from GEDCOM uploads, but plenty of them do. I have edited literally hundreds of profiles to move "created by GEDCOM upload" from Source to Acknowledgements, and adding the "Unsourced" program label.
I've started considering whether it might be worth the time to try and add dates to some of those profiles. I'm curious how many of that kind of profile we have on WikiTree. Anybody know how to search on that?
As to findagrave as a source, it really does vary. I've used it a lot for the LDS Mexican Colonias project. There's a huge body of connected and sourced memorials there. I don't download and copy the pictures and documents and text, because of copyright and permission issues. But I can say, confidently, that many of the findagrave profiles are better than WikiTree's with text from wills, diaries and obituaries, family photographs and tombstone pictures; many with attached images of sources such as death certificates & census records.
One place to be careful on findagrave is with the relationships. I find errors there from time to time. But when you have enough information, you can also add relationships, mostly in shared burial plots. One finds errors here on WikiTree from time to time, too. I often submit corrections an Ancestry.com, too, mostly because of errors in transcription on the index. And when there's a source like the Hale Collection inventory of Connecticut graveyards conducted during the New Deal, I give it some credence. Iowa had a WPA inventory during the 1930s, too. Those are IMO a credible substitute when a stone has gone missing in the c. 80 years since those inventories were performed.