Motte and Bailey tactics. "They might have a sufficient mass and delta v budget" is a very, very different animal from your previous position that military forces can be shipped as easily as supplies and mined goods.
No, don't shift it to silly rhetorical battles. It's not "they might have a sufficient mass and delta v budget". It's "if the technological-economical situation allows such colonies, then any government willing to pay for it *will* have sufficient mass and delta v budget". It will be just a matter of funding at that point.
Sure, you can argue that the defender's advantage in space will be considerable, much like in American Revolutionary War, but that won't help much when the colony in question is just few thousands of weirdos and the economic advantage of the founding country is measured in orders of magnitude.
In that analogy, just because the British Empire couldn't crush the rebellion of the 13 colonies, doesn't mean it couldn't crush a rebellion on the Pitcairn Islands.
Goalpost move, a submarine (which you were replying to) isn't capable of extracting resources like an oil rig.
Yet. I'd like to inform you that the same applies to space resource extraction so far.
In fact sea colonization is often something that is used as a comparison for the engineering challenges and economics to space colonization, in which some factors are very similar, minus the launch costs\tyranny of rocket equation.
You... do realize you just massively undercut your own position that the issue is technological and not legal/sociological there?
How are those mutually exclusive?
When technology barely allows the endeavor to function at all (or as currently it is, technology isn't there, in which case no effort is needed at all), even tiny, token efforts from the powers of status quo are enough to derail it. When technology and economy allows colonies to get bigger and more economically powerful, then it takes a lot more effort from the founding powers to hold them, and the colonies may slip away if they are in crisis or have better things to do.
They’ve already been doing this. Asteroid mining and powersats have been theoretically economically competitive since the Cold War space race, but we’re only seeing the likes of spacex and amazon showing up and progressing now, as automation technologies near the necessary sophistication.
No they aren't competitive, because the sufficient engineering isn't even there yet? If they were feasible, screw economics, world powers would absolutely want powersats because they are strategic scale weapons doubling as innocuous energy infrastructure, and they wouldn't hold back under the threat of competitors building their own first.