You need more then 8 cores. I would think a compelling mac pro product would have 24-32 cores.
Depends on what you're doing with it. If Geekbench is to be believed, the M1 with 8 cores is faster than an Intel i9-9880H, which also has 8 cores. And Apple sells Mac Pros that start at 8 cores and plenty of folks are doing serious work on iMacs and iMac Pros with 8 cores.