>Would that then allow the clients to operate at Data Rates >50% of the client max?
Let me make up some numbers to illustrate the point.
Lets say a client has 100MB of data to send. There is a fixed amount of RF airtime. If they send that data at 11Mb/s it will take twice as much airtime as sending it at 22Mb/s. The airtime can only be used by one client at a time. So by consuming such a large chunk of airtime, it leaves a lot less for everyone else to use, causing their throughput to be much lower, even though they might have a high connection speed.
Even one single client with a low-speed connection transferring data hurts the performance of every other client. Worse still - they don't even have to be on your WiFi network. They could be on your neighbours.
So typically you don't want to allow low-speed clients. A minimum bit rate of 12Mb/s is pretty standard these days.