Fortunately I'm the opposite of a videophile - I don't even know how High the Definition of our TV is. But I see your point, so indeed, a 4k dumb TV won't be able to show most Netflix content in 4k, correct? That's a major shame and pretty ridiculous.
edit: I just noticed that Netflix actually supports UHD on the Windows 10 app and on Microsoft Edge[0]. So running Windows on the media center PC appears to be a practical option.