Agreed that the 150°/300° is (also) because of hydraulic fire.
But AI certainly wouldn't certify you for TO with a temperature that is too hot for a RTO. Therefore, if you TO with 300°, AI must have made sure that you can safely absorb all brake energy in case of rejection. There might be one exception: If on your performance computer (runway table) there is a weight limit with the remark "brake energy", you run into this very problem.
As mentioned above by others, wear and efficiency are two different thing, and it is not that easy as you explain it. It depends heavily on the supplier of the brakes.
I was flying in a company where they had a graph of the brake wear in function of temperature: Cold brakes have minimal wear, when temp rises, wear increases to a max to around 300°, then wear goes down again until around 600°. It's a bell curve, or also called Gauss curve.
In other companies we had the information that wear is unimportant as long as you hit the pedals just once: Wear is a function of how many times you apply the brakes. How long or how hot or how strong is neglectable.
When you turn your view towards carbon brakes in Formula 1 car races, there is maximum brake efficiency with very high temperatures. You have certainly seen those pictures of cars driving by with glowing wheel hubs - that's the carbon brakes working.
In aircraft there are slightly different implications, since you have to cover the RTO case. It is better to have (relatively) hot brakes for wear and efficiency, but you don't want to have them too hot, because if they go beyond a certain limit, they get distroyed.
Therefore we have a perfect example for a balance of parameters. We have to make a compromize. Imho it is about 100-200°C. Others weight the danger of hydraulic fire, brake blast in case of RTO higher than efficiency and cost control. Be it as it is. I have made up my mind and stick to it.
Agreed also that this is an interesting topic.
Dani