Quick Update:
You'll recall that my OP asked about differences among streaming services for those of us interested in classical music. Specifically, I wanted to know if there were alternatives to Qobuz, at least until (if ever) Apple resucitates its Primephonic acquisition. You'll also recall that Idagio is the obvious choice for strictly classical, but that the other services offered the bonus of other genres for those days when only jazz or rock will do. Finally, I figure that if I'm going to have customer non-service, I might as well be dissed by platforms costing a few bucks less as by Qobuz.
I signed up for Amazon Music (the unlimited version, not the Prime cheapie) to try it out for classical music. The classical playlists and recommendations seem primitive relative to Idagio and Qobuz. The search function is at least usable now, except that the album results (for classical, "song" results are rarely what is wanted) are listed by title with teeny tiny thumbnails of album covers so that it often is impossible to know which of the listed titles is the one that you want. For example, if you are looking for the Oue recording of the Rite of Spring, you get a listing of several albums entitled "Rite of Spring" with no indication of which is the Oue / Minneapolis / Reference Recordings one. If the search is very specific, the first result on the list usually is the correct one, but still..... Finally, every time that a search is initiated, one has to choose between "Amazon Music" and "My Music"; I have only a vague idea why that happens and it's quite annoying after a few dozen repetitions.
I'm now poking around to see if Amazon seems to have recordings that Qobuz does not have. Amazon, after all, should have more leverage than anyone else around, thus a greater chance to host recordings from, say, Hyperion or RCA's back catalog. (For example, try finding recordings by Slatkin / St Louis.) So far, I've not seen much difference on the classical side, but I'll keep looking and report back.