What software are you referring to? What video are you referring to? What statement are you referring to? What I have seen are comments to ambiguous claims he's made. Given the ambiguity it's next to impossible to have a reasoned discussion.
That said I will take a stab at bringing less ambiguity to this discussion.
In his
Mac Studio ULTIMATE Comparison video he performs a CPU and GPU "torture test". In this test he provides benchmarks for the 24 core M1 Max, the 48 core M1 Ultra, and the 64 core M1 Ultra. The benchmarks consist of the time to complete the benchmark along with the GPU core frequencies (see the chart at time 22:44 in the video). In this chart you see the GPU frequencies decrease as the core count increases: 1,255MHz for the 24 core, 912MHz for the 48 core, and 752MHz for the 64 core GPU configurations. Based on the time to complete the benchmark was 7:14, 5:47, and 5:34 correspondingly.
To address your argument that perhaps the tasks didn't take long enough to tax the GPUs well, the shortest time was 5:34 which, IMO, seems reasonably long enough to ramp up to full utilization. If they didn't reach full utilization then why did the tasks take so long to complete? If they did why did the GPU speed decrease based on the number of cores? The answer to the latter has been seen before: Limited power means reduced frequency in order to distribute that power across a greater number of cores. It's the basis for "turbo" boost processor technology. Is this the reason? We can't say for sure but the explanation seems reasonable based on the data.
Now that we have a specific example I'd love to hear your, or anyone else's, thoughts as to why his conclusions are misleading.