Ideally, Chinese companies should hold the trademarks for hanfu and other cultural products. And they also take the initiative in popularizing it worldwide. That way if a foreign company tries to copy it, everyone would know who made it first and it would be an easy to win copyright lawsuit.
Problem with trademarking hanfu and other cultural products is its in public domain, maybe the could do a little alteration like Disney did with a lot of the movies based on older works, but stopping foreign companies from taking design and elements through legal means would be difficult.
If Dior popularizes it first, subsequent Chinese companies making a similar item would be seen as a cheap copycat, unfortunately.
For a while they'll regard it as a cheap copycat, until the support or defense from the fan dies off and we get to set the narrative. Perceptions of who owns the design or genre is very malleable, as long as the product listing is out there associating the design to China long after Dior's copycat product popularity dies off, the people would eventually associate the product with Chinese culture.
As for the Kdrama thing, don't expect anything intelligent from Kdrama fans lol. Fans often defend their product from any negative reception or opinion, even if its constructive or contradicts facts. The popularity of that show might have more to do with there being a big following for Kdrama, than because of the content of the show. What we can do to help Chinese shows of similar genre is localizing the works and creating a "pipeline" to direct new fans of the genre thanks to that Kdrama, into them.
A short explanation of what a "pipeline" is, you know why anime fans become associated with alt-right? because it have to do with Youtube algorithm giving suggestions like first you're watching anime, then it moves you to anime reviews, then anti-SJW videos from the same reviewer, anti-SJW cringe compilation, and all the way to Joe Rogan show. A lot of them got eased into those views, through some chain of association.