I think it’s more nuanced than that (although I’m sure we agree Raino).
Single core performance will help if you end up with a heavy process, or long chain of pretty heavy processing, where it’s all ending up on one core. So you could consider an audio track with a bunch of heavy plugins on it going to a group with more heavy plugins going to a master with heavy plugins. That’s one long chain of heavy processing mostly (or completely) landing on one core. You want a “better” core for that.
If you have a bunch of processing in parallel then more cores.
However, if you’re choosing between the 5900x and the 3950x then I would take the 5900x any day. Yes, it’s 12 cores instead of 16, but it’s got better cores than the 3950x.