You are complaining about Samsung's hardware being inexcusable, yet you consider an unnecessary software restriction to be acceptable? I was not aware that Amazon Instant Video, Netflix and Spotify had such restrictions but I do consider that restriction to be inexcusable and would use other software instead.
Google, Netflix, Amazon etc. are doing it for "DRM" purposes, sure it stinks but but Google pretty much dropped support for installing apps on SD cards from Android all together until it returned with Marshmallow, so even if you exclude DRM they can't even offer that functionally reliably on Android since not everyone is running 6.0.
If you are running Android 6.0 then you can use the SD card for phone storage if you format it as EXT4 and encrypt the SD card using the built-in encryption in Android which effectively locks the SD card to that device. This also prevents you from swapping SD cards in and out since it will break your apps and your phone basically.