They say reels sound better than cassette! Unfortunately you can't get the reels new anymore as far as I know. So the ones you have are precious and will probably become valuable over time <3

Cassettes are just very "low end" of the exact same tech, just like you have a ferari F90 stradale and a fiat 500
Cassette tape is 3.81 mm wide and speed is 4.75 cm/second, 4 tracks (stereo and side A/B) so an amazing less than 0.95 mm per track (due to the guard space between tracks)
Reel to Reel can be up to 50.80 mm wide and move up to 76.20 cm/second with a various number of tracks.
Digital is far better than any of their analogue counterpart . This apply to the technical ability of digitalisation like a CD, not to over-compressed streamed music and even less how things may have been dynamically compressed (see loudness war)

100% agree with you, especially on the lack of merit of compressed digital music.

My my... if this product was engineering today, you would never be able to put a BASF tape onto a Grundig spool, they would surely make a regulation to have a mandatory check made by the player to enforce the use of the same brand on each side, with validation chips embedded in the spool, and mandatory internet connexion to reject any compromised validation key.

Yeah they love doing that sort of stuff these days. I dislike the practice of forcing customers to only use same brand products.