I've been finding this side of the discussion very enlightening. My interest in a PS5 is more about making the games I currently own run better rather than buying new games, and it sounds like this isn't the case (unless the game gets a free PS5 update). I confess that this surprises me. Just another reason for me to just stick with my PS4 until a Slim PS5 is released.
Luckily for me lots of the games I play are improved on PS5. I didn't initially buy it to play games I already had, I saw that as a bonus and a reason I didn't need to worry about upgrading as I could play all my existing games.
Plus luckily games I play regularly like Warframe have full native versions on PS5 (which looks so much better than the PS4 Pro and performs way better). No Man's Sky also has a very solid PS5 version.
Most games benefit from faster loading and games like RDR2 and GTA V which I still play while not patched run at the best the Pro could do, solidly.
Days Gone is free on the PS+ collection so I will probably play it at some time if I get the time.
Hell even Elite runs 'better' with a more consistent frame rate.