I don't have nearly 4,000 UHD discs, but most of them cam with a HD blu-ray, one exception being a steelbook of Almost Famous.
The one that bugs me the most is the Jurassic 5-film set, there's a whole other case of blu-rays included, which is just taking up space.
I still have a lot of old sets that are BR/DVD in one box & in a few cases the DVD has more features, so I hold onto them.
Just bought UHD Running Man on Vudu & it has Zero bonus material, so I will be holding onto the DVD that's in a wallet of a dozen.
The UHD Lifeforce set I just bought last week, the only special features are on a HD blu-ray in the set.