Impression over substance seems to rule the day.
This is not really new. Fernando Lamas: "It is better to look good than to feel good." (Billy Crystal played the character "Fernando" on SNL as an exaggerated caricature). As (the actuarial statistics suggest) you will likely be dead long before the Gen Z'ers will, the goal for many companies will be to attract the Zs (which may mean flash over substance)).
What one person may consider wasted space ("white space") another sees as making something clean and defined. What one person might consider substance others may consider to be cluttered. Anyone who develops reports and has to explain things for a living will tell you that white space is not wasted, but actually very important. Personally I don't want just a bunch of text on a screen with no symbols or pictures (which has been suggested before). A picture, an icon, a symbol can provide a lot of information in a lot less space than a bunch of words. As a consulting engineer I like to stick to the tried and true KISS principal. There is no reason to make things more complicated than they need to be.
Not to say I'm a huge fan current UI, but I do like the simplicity of it. There are some vital features missing and the color scheme is a bit annoying, but a lot of the other systems out there (Plex) have too many layers and way too many words to make it a simple everyday user for someone who just wants to watch a show or movie.
You guys can discount me though because I am a month shy of 35
which makes me a Xennial not a Millennial or a Z BTW.