I'm not skeptical of Apple's M-series chips. They have proven themselves to be quite impressive and indeed quite competitive with traditional desktop CPUs even at very low wattages.
I'm skeptical of Geekbench being able to indicate that this specific new processor is robustly faster than say a 9950x in single-core workloads.
It's robustly faster at the things that Geekbench is measuring. You can find issue with the test criteria (measures meaningless things or is easy to game) but the tests themselves are certainly sound.