This demo is just fine for what it is: flatwound basses, vintage tones, direct, and a mic'd vintage tube bass amp. I do appreciate that it is "Vintage King", which obviously carries implications, but I do recall roundwound strings being widely used since the mid-1970s, and predominant since the 1980s.
Given that so many bassists use roundwounds, I don't think it's beyond the pale to include something with rounds. Pretty simple. Does that mean I like a demo video with only pop/slap? Nope. I hate them, too, for the same reason: too narrow of a demo. Does that mean I prefer a demo using roundwound strung basses that go clickity-clakkity? Nope, but that doesn't mean that neither pop/slap or clickity/clackity has no value to anyone out there, even though it might sound insipid or lousy to me.
Look, I'm just calling it like I see it, and unless Vintage King/API are 100% fine crafting their videos in such a narrow fashion, that's up to them, and perhaps that's exactly what they want to project in a video. IMO it just doesn't demonstrate the preamp's capabilities across the broadest tonal and stylistic spectrum, that's all. It would be nice to see them demo a roundwound strung bass, though...even if there is no justifiable reason to do so.