I actually think they have some great content, and a pretty decent app. Their “originals” especially are pretty great - Fleabag, the Boys, the Expanse, all excellent. But yeah, the quality of the app is a bit lower than some of the others, and they have a lot less content than Netflix, because Prime is really not a main focus of their company, more of a nice add-on.
I assume Netflix ships a much lower level integration that doesn't rely on nearly as many of the TV OS's api's and therefore can launch even when Prime has decided to bork the whole system.
Disney streaming is pretty good, but the UI isn't as good as Netflix for use across the room. Why do they make the title cards have second level text that is so small it can't be read, and then not have the continually updated preview that Netflix does?
I agree Amazon is pretty disappointing. It seems more like a dodgy pirate video player than a major competitor.
There's a setting for language on the web, but it only affects web.
In my case I'm a foreigner who is still learning the local language, but it must be a real nuisance for people in multilingual countries like Belgium or Switzerland where I guess it would just go "oh, Swiss IP, I guess you want German then".
The firestick remote replacement app (because I can't ever find the actual remote) is also a joke: it disconnects all the time, fails to reconnect and it is generally not very usable.
HBO, Disney, Hulu, Apple etc. are all somewhere in the middle, and yes Netflix is FAR ahead of the pack.