Differentiate between 4K and High Dynamic Range. The two are bound together currently in UHD discs, but there is nothing to say you could not use HDR, Dolby Vision or HLG on lower resolutions, it would just require a different codec than is currently used for those formats.
4K Tvs are 4K all the time, regardless of the source. So watching a Blu ray or 4k Netflix is still effectively 4k for both on the 4k TV, just that one is up scaled. Netflix uses a higher compression/lower bitrate for 4k than blu ray so any differences maybe hard to spot and there could be compression artifacts visible on either. Whether you see a real improvement with 4k largely dependent upon the viewing distance and quality of the media. Blue Planet looks gorgeous in 4k or 1080p. A number of the current and reissued 4k material is in fact just up scaled. New films, last couple of years have been filmed in 4k or even 8k so it should be 1:1, Harry Potter or Star Wars reissues are not true 4k and the mileage may vary between discs.
High dynamic range, be it HDR, Dolby Vision or HLG is a lot more noticeable than simply 4k. The peak brightness required for true HDR is several thousand nits. Oleds are usually around 400-600. The best currently is around 1000 nits from things like Samsungs QLED and others. So still less than the ideal but more than bright enough from most homes, especially if the ambient light is controlled. Netflix Mindhunters burns my retinas everytime a city location is displayed. Again like most reissues, the quality and benefits of HDR are media dependent.
Here is a list of viewing distances for upto 85" so you can get an idea from this. I am just about on the cusp with my 55" @ around 6-7'. With the 100" 1080p projector I am well inside @ ~10 feet.
https://www.crutchfield.com/S-7qIE2pL2u7I/learn/learningcenter/home/TV_placement.html
This is amusing but don't take it too seriously
Oh and when he talks about file sizes he is talking about actual individual frames as a total. Compression makes this a lot more manageable, however it can be taken too far and introduce its own problems.
By the way Disney wasn't always like this, phase 1 and 2 Marvels are fine. Just don't expect much from Infinity War, Solo, or Incredibles 2. I wish/hope they will sort this. I started to notice it with Guardians 2, then Last Jedi, Thor and Black Panther.