But a 7950x is just a 7900x (They have identical silicon) that is just "lucky" enough to survive more power draw. If you make the TDP the same you just end up with the same CPU
Are you sure? The 7900x has 12 cores, while the 7950x has 16.
They disable some cores? How else would you explain the lower single core performance?
Pretty sure 7900x has fewer cores/threads.
Anyway fewer turned on? They need something to sell when one or more of the cores don't work. Would be nice to let you have 15 cores when that many of them work.
Turned on? Pretty sure this isn't like Phenom where 3 out of 4 cores worked. And you can enable them via BIOS.
I did read that the silicon that can take higher voltages is worse in lower power (i.e. lower voltage) situations.