As someone who professes knowledge you obviously know that all listings and sides do not belong to the agent. They belong to the broker and agents are employed by the broker.
The reason I stopped using my sister in law for the purchase of my properties is because she works for Coldwell Banker. Most brokerages do not allow agents to do what you are suggesting. Nor do many of them allow commission rebates. Most agents get nowhere near what people think they get. Imagine a typical agent working for a large brokerage gets a split of the commission. So does the broker, so does the corporation.
Conversely the fact that so many people here have agents yet post questions and queries here that SHOULD BE directed to the agents says that people are content with substandard quality due to family relationships, friendships or whatever. They tolerate it and put up with it which consistently befuddles me. similarly I can never figure out why so many people pay full commissions when they sell or do not demand rebates from the agents when they buy but that is the way of the world. That is why the large traditionals will never die. People put up with it and always will. This is why brokerages want agents, lots and lots of agents.
Jimmy is a good example. He is a good guy and posts here alot. Lots of queries and such, and here is a sister in law telling him now is a good time to buy when that is a crock of sh-t. Yet he will most likely use her in order to reduce family stress.
I agree with your point that nepotism or a hybrid of it should indeed be rewarded with lower rate. However it may be physically not possible to do so. Just wanted to point that out to you.