plus, ships can fly out of the gravity well (how else do you keep your cariers away form the pirate turrets), just not that far. they need to be close to the circle to jump out, a buffer zone. Haven't you seen ships fly back just to turn then jump?

if anything you'd use an ability like this to halt an opponent jumping out. to make them return to the buffer area and getting caught by your defences as they try and run

Technical problems aside, I love the concept.

There's an old science fiction novel back in the 60's that had ships with an "exponential field".  When flipped on, it expanded or shrank space so their weapons could be brought instantly to bear from extreme ranges or space could expand to move them out of enemy range.  Over time, the quantum state of the ships was put out of true from the distortions and the computers would begin to calculate incorrectly making the ships worthless.