The sump is fed by gravity from the display tank. The display tank is fed by the return pump.
As long as your overflow and plumbing are sized correctly, the return pump basically handles what goes in/out of the sump. If the return pump is doing 1000gph, then the overflow and drain will also be 1000gph.
Ever take a shower? How do you balance the water coming in from the shower and the drain going out.
You dont.
A tank works the same way. The drains should be able to handle more flow than goes in.