Maybe you’re right, but I remember than in the 2000s I’ve had identical cpu heatsinks in both copper/aluminum versions, and the aluminum one had better performance. And then they started to make hybrid ones, stating that the copper part was to allow rapid heat transference and the aluminum parts to improve dissipation. But maybe it was all marketing.

Copper is better conductor but it’s worse at dissipation. Do the experience yourself, heat a block of each and then touch them afterwards.

Why copper? Aluminum works way better as a dissipation surface.