All they do is take the real skill out of fighting, the game was a scary place before cell recharges.
If you can't kill a ship that is using shield cells, either you're not keeping the ship in front of you to keep fire on it enough (meaning you need practice at dogfight maneuvering) or you're not keeping your guns landing on target (meaning you need practice aiming).
In a matched fight, shield cells only mean an extra few seconds of life. They don't charge the shields very fast. They don't KEEP shields charged or make the target invulnerable. If it's taking you long enough to kill a target that they have a chance to fire a second shield cell, either you are seriously out matched or you need practice. Complaining that shield cells are broken when in fact they're weak and don't turn the tide of battle in an even match, just advertises that you need more practice.