Just about everything you want is magically not available on the normal amazon music.
I find that Alexa can be a bit hit and miss when trying to find albums on Amazon Music, sometimes claiming you need Music Unlimited for albums that are actually there on normal Prime.
I think if you add those albums to “My Music” (free) then she suddenly does a much better job of finding them.
You get 2 million with Amazon Music (free one) sounds a lot but rather unsurprisingly it is quite poor.
It’s not great. Pink Floyd but no Led Zeppelin.
But they probably have enough Dire Straits and Status Quo to keep the dads on here happy 😉