Correct, some of these streaming platforms have agreements with certain content providers.
It's all about the 'skin' or user interface (how you interact) with layout, use remote versus phone, and the content chosen or available.
Firestick is like the old Chromecasts which is plugged via USB.
I found it restrictive with content, versus Roku private channels in research. Id planned to jailbreak a FS, then got sidetracked. Wanted to buy one, then saw the $.
Roku seems like a more open platform. And, it isnt Amazon.
(One negative on Roku is they get into content Wars sometimes with providers, instead of negotiating they just flip the bird).
But my stock holds fast.