The overcompression/poor compression of streaming video is scandalous. Netflix cannot even offer a decent DVD quality stream, it seems perverse for them to even offer 4K.
Where streaming services do fall down for me is audio stream handling. If you stream high quality in most services on most dedicated streaming devices you get 5.1/7.1 by default, with awful, unconfigurable downmixing to 2.0/2.1 that makes you crank the volume to make dialogue audible but is still immediately drowned out by the slightest peripheral foley effect. Amazon video is the worst about this.
I still haven't seen any streaming service look nearly as good as a Blu-ray and this is on a mid-range TV, from farther away than I should be with probably-should-wear glasses vision.