I was doing similar calculations for an A-380 but I doubted my results as they pointed to rate of energy recovery being in the order of a small power station for 10 seconds.
Which probably means that your calculations were correct, it has to dissipate energy at a rate of at least
dozens of megawatts.
Max landing weight of an A380-800 is 391000 kg, landing speed around 140 knots (72 m/s) - note that
this is airspeed, so ground-relative velocity can be slightly lower. Still, the hardware has to be designed to
handle the maximum case.
This results in a kinetic energy (1/2 * m * v^2) of nearly exactly 1 GJ.
So to stop in 10 seconds, energy dissipation has to happen at a rate of 100 MW. Douple the stopping time,
and it's still an impressive 50 MW.
A single brake on an A380 wheel can handle a 5MW braking (once, in an emergency).
An A380 has brakes on 16 of its 22 wheels. Add the other deceleration systems (spoilers, reverse thrust),
and a complete A380 can probably dissipate kinetic energy at a rate of a considerable fraction of a
gigawatt in case of a last second rejected takeoff (faster and quite a bit heavier than the worst-case landing).
That isn't a small power station anymore.