Perhaps FIOS is still atypical. 300Mbps/75Mbps is what I've got. Pity I can't get 300/300.
That is not a counterexample. 300Mpbs or 75Mbps are not standard ethernet speeds. To do QoS at those speeds you are either at the mercy of the provider-controlled CPE or you try to shape your traffic in your own router. Either way you are into territory where you can make it work, at least with some routers.
This is very different from the situation at 100Mbps or 1Gbps where QoS tends to work just fine without special configuration, except for enabling it on those devices that have it disabled in the default configuration.