1% from a Dyson Sphere would be a better energy return than 100% efficiency from any conventional energy sorce. Similarly, 20% from solar is competitive with 60% from nuclear, 50% from coal, and is easily better than 100% from my neighbor Dan riding a bicycle powered electricity generator.

You can't cite efficiency percentages in a vacuum to imply they are a better or worse than alternatives, because those aren't percentages of the same kinds of things, and they don't tell you about the economics, production in absolute terms or EROEI.