I have no expertise is this area, so I'm not getting into whether or not this idea makes sense.

That being said, this statement strikes me as missing the point:

> Solving cost of launching mass has been the entire premise of SpaceX since day one and they have the track record.

As I understand it, SpaceX has a good track record of putting things into space more cost effectively than other organisations that put things into space.

That is not the benchmark here.

It doesn't matter if Musk can run thousands of data centres in space more cost effectively than (for example) NASA could. It matters whether he can do it more cost effectively than running them on earth.

The cost of "launching" mass on Earth is not zero, though.

I don’t think that statement was missing the point. As you point out, what matters is the total cost of ownership of the system. The cost of launching mass into space today isn’t the only reason terrestrial data centers are more cost effective today, but it’s the main one. If you make it cheap enough to send giant solar arrays and radiators to space, the other costs of operating in space may start to look like a small price to pay to eliminate the need for inputs like land and batteries.