I think you're correct on both counts. With the plugins running on separate cores, they wouldn't be trashing each other's caches or branch predictors, so they might actually run faster and offer lower latency than stacking them all onto a single core... but odds are low that the difference would be significant.
The main advantage is that you wouldn't be limited in the number of plugins you could run by the performance of a single core, since you could run each plugin on its own core, like you mentioned.
Obviously, having faster individual cores means that each plugin introduces less total latency, but the difference in single-threaded performance between Zen 2 and Intel's best is likely to be very small, and I fully expect Zen 2 to have the best single-threaded performance in certain applications.
You wouldn't want to run a plugin on each core, you would want to run a chunk of samples on each core. Then the data is staying local (and the instructions aren't going to change so they will stay cached as well).
The main advantage is that you wouldn't be limited in the number of plugins you could run by the performance of a single core, since you could run each plugin on its own core, like you mentioned.
Obviously, having faster individual cores means that each plugin introduces less total latency, but the difference in single-threaded performance between Zen 2 and Intel's best is likely to be very small, and I fully expect Zen 2 to have the best single-threaded performance in certain applications.