Like I said.... people argue about it. Partly because so many don't believe that most motherboards actually have in practice the result of the same speed previous gen as half the current gen.I've gone through several generations of these articles in quite a bit of detail, including this one. There's no place where "PCIe5 GPU in a PCIe3 slot" results in "10-30%" performance loss. You have to also cut the lane count, in order to see such a drastic performance reduction. Like I said, bandwidth is bandwidth.
They certainly did try cutting lane count.
And the results in terms of performance loss are always starker for lower end hardware.