Maybe there is some extra something that Roon needs, but I’m quite confident spotify integration is possible. Actually, it’s not hard to download a Raspberry Pi Media Player with Spotify support, which works quite well. Going into my spotify account gives me a list of all the systems I have given permission to integrate with, including my Sony Phone’s native music app. If Sony can do it, it must at least be possible. So i don’t think that particular excuse is a valid one.
I agree, Tidal put’s a lot of focus on the Genre similar to it’s owners own brand, but there’s a lot missing and it’s also an awful lot more expensive.