Is the "but at that kind of energy output we'll boil the planet" limiting case really a hard limit though?

If we're at the stage of having super-dense energy sources and super-tech, couldn't we we use those to cool the planet effectively?

Use a heat pump to move that heat off-planet? Drop some icy asteroids in the seas? Take compressed hot atmosphere off-planet in super-blimps, run it through a heat exchanger on Titan and then bring it back?