>people have already built most of those microwave tower paths here on earth
I can assure you that lucrative paths like New York-London and New York-Tokyo have not been built yet. In fact, the vast majority of lucrative trading paths have not been built yet due to geographical restrictions. Yes, fiber optic links exist, but those only go up to 0.7c.
To a trading firm, the choice between a satellite link that does ~0.9c and a fiber optic link that does <0.7c is obvious.
That all depends on Starlink supporting point to point inside their network. Also that path will be more zig-zaggy than the great circle fiber path and importantly will vary during the day as the satellite tracks shift relative to earth. [0]
[0] Unless their in a harmonic orbit I guess not 100% sure abou that one. There should always be some jitter in the connection time just from the satellites moving even if their ground tracks are very stable.
I can assure you that lucrative paths like New York-London and New York-Tokyo have not been built yet. In fact, the vast majority of lucrative trading paths have not been built yet due to geographical restrictions. Yes, fiber optic links exist, but those only go up to 0.7c.
To a trading firm, the choice between a satellite link that does ~0.9c and a fiber optic link that does <0.7c is obvious.