The amount of time spent on the brakes is the most important thing which dictates the wear of carbon brakes, not the amount of energy put into them (which is the case with steel brakes).
By braking harder, you are spending less time on the brakes in total, which means that you will have less wear on the brakes. Let's just imaging you wear 1/10000th of the brake every second, no matter how hard or soft you brake. By braking lightly, taking 20 seconds to stop, you'd wear out 1/500th of the brake. But if you only took 10 seconds, you'd wear just 1/1000th of the brake. While it's not quite as simple as that, that's the general idea of it.
Another contribution factor is the non-linear and non-proportional correlation between brake wear and brake temperatures. While this is slightly counter-intuitive, brake wear increases until about 200°C disk temperature (note that indicated temperature is usually lower), then it actually decreases from there until it becomes much hotter (about 700-800°C). So, by braking harder, you will also heat up the brakes to the point where brake wear is less than by braking lightly.
Because of this, it's better to apply the brakes in one go, to reduce the total time on the brakes. Boeing's excellent article on the Operational Advantages of Carbon Brakes gives the following advice when taxiing:
Taxi braking recommendations for carbon and steel brakes
Because the wear mechanisms are different between carbon and steel
brakes, different taxi braking techniques are recommended for carbon
brakes in order to maximize brake life.
Steel brake wear is directly proportional to the kinetic energy
absorbed by the brakes. Maximum steel brake life can be achieved
during taxi by using a large number of small, light brake
applications, allowing some time for brake cooling between
applications. High airplane gross weights and high brake application
speeds tend to reduce steel brake life because they require the brakes
to absorb a large amount of kinetic energy.
Carbon brake wear is primarily dependent on the total number of brake
applications — one firm brake application causes less wear than
several light applications. Maximum carbon brake life can be achieved
during taxi by using a small number of long, moderately firm brake
applications instead of numerous light brake applications. This can be
achieved by allowing taxi speed to increase from below target speed to
above target speed, then using a single firm brake application to
reduce speed below the target and repeating if required, rather than
maintaining a constant taxi speed using numerous brake applications.
Carbon brake wear is much less sensitive to airplane weight and speed
than steel brake wear.
These recommendations are intended as general taxi guidelines only.
Safety and passenger comfort should remain the primary considerations.