I don’t have two great devices to test with but my bet is on the CPU being the bottleneck. I have only used the feature between my desktop (5900x, 2,5 gigabit connection) and a steam deck (a comparably bad CPU, 1 gigabit ethernet or WiFi)
The steam deck also caps at around the same speed when downloading from the internet while the desktop can download at near 2,5 Gigabit speeds.