When we get into genus Homo, it seems like the normal rules for what "species" means morphs. If our ancestors and neanderthals and denisovans could produce viable offspring, we're not separate species, we're separate subspecies. We're genetically as different as different kinds of corn or different kinds of tulips or different breeds of dogs, it's not corn vs tulips or dogs vs cats.
That said, I'm inclined to agree with you. Those old DNA samples presumed to be contaminated human or degraded human .. my guess is a lot weren't. I think those samples were good enough to have separated human from chimp for example. People doing the testing / paying for the testing were looking for something akin to an African ape .. orang, gorilla, or chimp .. and weren't ready to accept that DNA 98% towards human on the piece of the scale separating human from chimp, which already were 98% similar .. at least in the sections that are tested to identify species .. could be correct.