Is the advantage of wagyu and other fine beef obliterated when formed into minced burger patty?
The main thing that wagyu is supposed to get you is dense marbling. That's especially important for cuts low in fat, like the filet and the sirloin. That is, steaks.

The rest of the cow has to go somewhere. The parts that get ground into burgers on conventional cows might as well go into "Kobe sliders". There will be some differences from conventionally-raised beef, where the ground meat is usually made by combining fatty cuts with lean cuts to achieve a precise fat ratio. I would expect ground wagyu to have more fat than a conventional burger, and to have the fat incorporated somewhat differently, but it will vary from processor to processor.

So I'd say that the advantage isn't obliterated, exactly. I'd just say that a wagyu burger will be a lot more like a regular burger than a wagyu steak compared to an Angus steak. There's nothing wrong with that, at least as long as they're not trying to charge massively superpremium prices for it. (In my experience they come with a modest upcharge.)