The thing about proportional pricing is that it doesn't scale up or down. Assuming your sale was near the median US home price, the seller's agent would net around $12k for their work. You believe that was worthwhile, let's assume that was money well spent.

Suppose the market was hotter when you sold and your property was worth 2x the median. Is the same work worth $24k? What if you sold in a hot market in a hot neighborhood, which should make it somewhat easier to move the property? Does it make sense that this would increase the amount the agent gets paid?

For similar reasons, proportional pricing doesn't work well at the lower end of the market, where listings are often under $100k.