The majority of kits pretty much always (certainly from since I'm old enough to remember Lego catalogs) had "a model" to build, the "bucket of pieces" packs always were just a small part of it, and you always could use the pieces of the former to build anything (with some themes obviously having some less universally useful pieces)

Not when I was a kid. The co-branding kits came later. And have changed the nature of the product, as well as the minds of those who use it.

They’re all Lego pieces. Putting a picture on the box doesn’t make them any less creative.

So you play top dollar for a Death Star and you build what, a basketball? Why waste the money?

You pay top dollar for the 3,800 pieces—which you can assemble in any way you want, just like any Lego pieces in existence. I really am wondering if you’ve just never played with legos before? If not, buy a set—they’re a lot of fun, and you can start with a plain box of pieces for $5 to $10, no need to jump in the $750 deep end.