And?
You just attach MORE ion thrusters onto a bigger rock. Same deal.
What I'd posted is fundamentally how "space mining" is going to work. NO ONE is going to "send a bunch of guys" out to the asteroid belt, where it'd take years to get there, years to get back, and another year or more just to mine stuff. They'll send robotic probes out, to attach thrusters to the rocks and send them our way.
I'm simply informing you that it's MUCH cheaper to send them down onto some poor or unpopulated area of our planet, vs trying to capture them in orbit and work on them in space (or on the moon). Moon might be an easier bet.
But your apparent conception that we'll "head out into space to do onsite mining" is just silly. You'll send the rocks back to Earth, just like I told you we would.