Spotify does that and it's a complete deal breaker.
I want to log in to all my home devices _once_, with a single account. Not continuously log out and log in and try to type complex passwords with a remote control. I mean, I can't even play different songs on different Google Homes or different TVs with Spotify, unless I sign in with different account on each - and then each device is stuck with a specific set of playlists. Horrible.
Netflix's system has worked out brilliantly for us - we have half a dozen TVs, and any member of the family can watch anything they want on any TV with their own preferences and profiles with minimum hassle.
Again, the use case is different.
What you describe: If you are an individual, ability to login same profile on many devices is sufficient (both netflix & spotify do this).
I'm talking about family use-case with multiple devices.
With Netflix, my wife, myself, our kids, anybody, can click a profile button on any of our devices (TV, tablets, phones, etc) and simply continue watching what they were watching, get their recommendations, etc. Crucially, they can watch different stuff at the same time on living room TV and basement TV, with no hassle.
I have opened support cases and there is currently no way I'm aware of to do that with Spotify. I have Google Homes in all the rooms, and I want to seemlessly play different stuff in different places. To do that, I have to create as many accounts as there are devices (that's a LOT!), AND each device is now locked in to their playlist/song/etc.
The underlying difference of paradigm is: 1. Netflix - single account with multiple soft profiles. You can watch as many streams on same account as you paid for, hassle free
2. Spotify - multiple accounts loosely linked solely for purpose of billing. Each account can not stream multiple places. So if you want to stream something on three devices in parallel, you have to a) Create three accounts; b) log in separately with those accounts in each device. What when I have dozen devices? (4-6 Google Homes, 6+ tablets and phones)? It is now insane to do anything.
Basically we now exist as isolated islands and have given up on listening to music in kitchen and family room at the same time. This is awful.
But anyway, I only have one screen, so it's still the case that Netflix charges considerably more just to receive UHD content. As price discrimination goes, that's a pretty scummy way to do it. They've shot and produced this content in UHD, yet they give a much lower quality version to their base customers. I know they have every right to do that, and it might make business sense for them (since people with UHD TVs probably have more disposable income), but it has always felt scummy to me.
Almost every other video service globally does, and of those you mentioned Prime's pricing is mostly based on shipping, Apple TV+ at this point is effectively a PR campaign and not a proper service, and Disney+ is running at a massive loss leader to build share.
Netflix isn't charging a sustainable amount of money as it is. You should probably think of it less as charging more for UHD as offering a crazy discount for lower content quality.
You could just watch it in regular quality - it's not that bad. Either you feel UHD is worth the extra $3/month (honestly a pittance compared to the price of a UHD TV) or you do not.