[kibwen]

The efficiency of stellar fusion doesn't matter, only the cost does. Whether or not humanity decides to harvest it, the sun emits a ludicrous amount of energy for free, just waiting to be captured with today's tech.

Of course, you'd never want to actually use a Dyson Thing to ever transmit 100% of the Sun's energy to Earth, because all energy turns to heat eventually and you'd scour the planet clean from all the inevitable waste heat.