I don't think that's very much alike at all. Denying the existence of a major dynasty is like declaring that Abraham Lincoln and Andrew Johnson didn't exist, and all the historical traditions and documents to the contrary were invented to cover up the two terms Jefferson Davis served in the White House. I've never seen even the most strenuous Lost Cause advocates say something like that, because why in the world would you?
> Denying the existence of a major dynasty is like declaring that Abraham Lincoln and Andrew Johnson didn't exist
There's a great difference of scale.
Lincoln died about 150 years ago. There are voluminous primary sources about Lincoln - e.g. photographs of him, original documents that he wrote, firsthand accounts of his actions, etc. We certainly don't know every detail of his life, but we do know a lot of it, and we're quite confident it's true.
The Tang dynasty, by contrast, fell over a thousand years ago. We know of it primarily through second- and third-hand histories and through interpretation of archaeological artifacts - much like our knowledge of Greek and Roman history, for instance. There are a lot of thinly covered areas, and many of the sources are biased; there's a lot more to be uncertain about.