FWIW, this is only true for newer hardware. ie if you plugged in a pcie gen3x16 device into a pcie gen4x8 slot, although the bandwidth provided is in the same ballpark, the device will only run at pcie gen3x8.
So we'll need until the devices upgrade themselves to gen4 in this scenario to make use of higher bandwidth.
Not all pci-e lanes on your motherboard are created equal: Some are directly attached to the CPU others are connected to the chipset, which in turn is connected to the CPU.
It's possible to convert a single 5.0 x16 connection coming from the CPU to 2 4.0 x16 connections.
I expect consumer machines to keep doing some conversion and expansion in the chipset, but nowhere else. I expect servers to directly attach almost everything and drop down to smaller lane counts for large numbers of devices.
It's worth noting that when Kioxia first put out PCIe 5.0 EDSFF drives, they were marketing them as being optimized for 2 lanes at the higher speed.