Works fine for me. Here's an asymmetric circuit being "battered" by a dozen uncapped torrent uploads while maintaining guaranteed throughput for VOIP calls and latency for gaming with nothing but layer 7 QoS on a £5 consumer router.
Average ping never more than two or three milliseconds off baseline.
Left is is while idle, right is while running a dozen simultaneous FTP uploads.
Does not work my arse. And this is using a router with a supposedly crap QoS implementation.
And for some reason you seem to think layer 2 policing and QoS are somehow different things. Whether you throttle based on a layer 2 address or a layer 3 address it's still the same damn thing. The only difference is that there's absolutely nothing you can do with layer-2 QoS rules that you can't do better with layer 3 to layer 7.