I can answer that! I had over 1000 CD albums ripped to FLAC. If you ignore old CD singles (which realistically, you wouldnt expect a streaming service to have many of when they were released more than a few years ago- or even 30 years ago). Around 5% of the albums arent on Qobuz- Tidal has even better coverage. I'm not saying they will be exactly the same version of the album of course, the streamers tend to have only one, or maybe one plus a "deluxe" or "remaster".
As others have said, Roon is perfect as it allows you to seamlessly merge streaming and local files, it hiding any duplicates and defaulting to what it things is the highest quality version (assume thats bit depth and sample rate, not which actual version).
Moving between streaming services is very easy with a 3rd party app like Soundiiz- you can transfer libraries from service A to B for around $25 annual fee. Impossible without.
If it helps, like I said, I had over 1000 CD albums, then I started downloading new music not buying CD and got to around 2000 . Then around 2 years ago went to streaming and have over 5000 in my library.