If you care about benchmarks, a Pi4 will score around 200 points (1 core) or 550 points (4 core) at 1.5GHz on GB5. At 2GHz you can reach around 700 points multi-core.
Ryzen 2700 will easily go above 6000 points in multi-core bench without overclocking.
So even in a theoretical, embarrasingly parallel workload with minimal sharing between cluster nodes, the Zen will be faster than eight pies. It's not even a contest if you also need some I/O, shared memory, or heavy SIMD.