The ceiling on asteroid mining is orders of magnitude higher than anything constrained to earth. Put another way, imagine if you owned Australia because your company built it up off the ocean floor.
The sphere does not need to be built or owned by a single entity. You too can own a single unit of the sphere for the low, low price of $2T. There can be different corporate entities owning different sections and monetizing it in all kinds of ways (e.g. the KY sector is ideal for powering asteroid mining in the Kuiper Belt)
I hear people often talk online saying energy in the future will be either free or very cheap.
Dont know what cheap means for them, but it will never be for free because abundance happens when the supply exceeds demand and I dont see the scenario where the demand for energy is declining in a long run.
Well, I guess the argument would be that a billionaire financing the construction of space habitats could make them effectively company towns, but of a highly educated workforce. Once enough of them are there they'll have their own economy, and whoever owns them/the oxygen supply/whatever would be getting a lot of return. I don't think that's a great argument, though, for multiple reasons. I think it's better to just frame it as building a legacy. Put humans in an entirely new place that many of us desperately want to be, end up having the equivalent of a city named after you.