Hey there @Mb101
Deezer can certainly be streamed to Alexa/Echo devices; I am doing it right now. I just asked Alexa to play my Flow on deezer on my Echo Studio and it’s happening.
Or do you mean casting rather than streaming?
Because of the services you listed, only Amazon Music will cast to Echo devices. Spotify can also use Spotify Connect to control the stream, but Tidal will not (there is not even an Alexa skill outside the US), YouTube Music is completely incompatible, and Pandora needs voice requests like deezer.
I can also AirPlay deezer to my HomePods and to my Sonos speakers directly from my deezer app. It also works via CarPlay, so it’s not limited to headsets and earbuds.
Was this just a bit of a dramatic license or are you confused?