I must say, after 2 days of listening to all sort of content on Tidal, surprisingly all of which was HI-FI, the sound quality is rather good, but doesn't compare with CDs ripped to FLAC and played through fb2k.
I can't even put my finger on the differences, but it's like fb2k has a more crisp sound, a little clearer, and most of all more "alive".
This is true both for the web player and for the windows app.
If the files are indeed lossless, I guess the problem is in the playback software. Which is weird, because honestly I never noticed much difference between different players on Windows. Otherwise, something's fishy...