Not every pilot will want to prolong the encounter - the shield cell is a defensive module and can be used to assist the pilot when they wish to flee.
This is true. The lesson I think is to double check who you're up against. Don't forget your Sun Tzu, "the victorious strategist only seeks battle after the victory has been won, whereas he who is destined to defeat first fights and afterwards looks for victory." Or, "He who knows when he can fight and when he cannot will be victorious." Or, "It is said that if you know your enemies and know yourself, you will not be imperiled in a hundred battles..."
As for prolonging, "What is essential in war is victory, not prolonged operations." And, "There is no instance of a nation benefiting from prolonged warfare."
Basically, every battle is already won or lost before it is even fought. So, my suggestion is to check a potential opponent's modules before engaging. Assess your enemy, Sun Tzu says, "It is the rule in war, if ten times the enemy's strength, surround them; if five times, attack them; if double, be able to divide them; if equal, engage them; if fewer, be able to evade them; if weaker, be able to avoid them." If you're out of you're element, you need to flee, preferably by not running away, but pulling a Han Solo and turning into the enemy to reduce the time he has to fire, whilst engaging the jump drive.
So, on topic, I agree shield cells are needed for smaller ships to have a chance of escape when they are outmatched. It might make PvP tedious in larger ships, but then again,
it took three hours for the USS Monitor and the CSS Merrimack to fight to a standstill.