1 - look at the people onboard the USDZ format (pixar, adobe, autodesk, epic, etc.). This is geared towards getting designers to bring in high quality 3d from the the first step of the pipeline.
2 - Just because apple uses the format doesn't mean they don't optimize it for display. I have no idea what happens behind the scenes, but if they could make PDF work well for a desktop, then I have faith in them. Look a this link [1] and the video [2] from a YEAR AGO. It seems to support my thoughts (via the Unreal Engine). The second paragraph is the key.
I understand your concerns, but I truly believe that in two years, you will look back on this and say, "yeah, they figured out how to get this to work well." Of course, I am wrong occasionally, too :)
[1] - https://www.cinemablend.com/games/1631230/why-two-disney-fil...
[2] - https://www.polygon.com/2017/3/1/14778602/epic-gdc-finding-d...
The example you given is actually irrelevant for consumer use cases. For consumers, loading speed matters. They are interactive apps. They can't spend too much time loading. While for film studio, they are batch rendering scenes. Loading speed is a lot less important.
As other posters have commented here, glTf is the current best practice for runtime delivery formats (and, by extension, glTf would be a terrible choice for author-time DCC Data exchange, for exactly the same reasons as why USDZ is better suited to authoring than delivery).
Moore’s law and computers getting faster won’t make USDZ a good runtime format. glTf will remain the better runtime format and USDZ will remain the better authoring format, because that’s what they were designed to do well. As someone else observed, it doesn’t matter how fast your browser gets, no one is going to recommend you populate your website with PSD images, because PSD is an authoring format not a delivery format (and likewise PDF is an equally terrible authoring format but a great delivery format)