To start battleships do not "get in close and unleash hell" since ...ITS STUPID BEYOND BELIEF!
You have RANGE so WHY IN GOD NAME YOU ARE GOING TO CLOSE IN WHEN YOUR BIG GUNS CAN HIT THE TARGET MILES AWAY?
Stupid beyond belief, yet has been used in many SCI-FIs, real life battles, Even in Mass Effect.
Why did the Geth Cruisers/Dreadnoughts and Frigates get in close to the Destiny Ascension when they could have blasted it from a very large distance? Why did the Alliance Fleet surround Sovereign at very close range, while the Normandy Itself was flying around at point blank range until the shields went down?
Why did Shepard order Joker to get in close, even with the Thanix, to finish the collector ship?
To also exemplify with a real life battle. Why did Nelson engage the Spanish/Franco fleet at Trafalgar at POINT BLANK range? Why did he sail his ships through enemy cannon fire, taking heavy damage, just so he could get close to them? A plan which most thought was insane, and yet was one of the greatest victory in naval warfare to date ( 21 ships captured one sunk, and no ships lost )
You cannot compare Starship Warfare against Reapers to that of 20/21 Century naval warfare. A torpedo in real life can do serious damage to a ship, in ME universe? Not so much. Nor can you compare the fact that aircraft in the modern world can sink a ship easily, when in ME a fighter can't do squat.
In a battle against the reapers, if you stay at range and fire your guns, you ARE going to get decimated, ( the reaper main gun will shred your fleet in seconds ). In order to survive you need to get in close so that their main guns are infective, and then use your broadside guns to blast at them, and for your shields and armor to be able to survive their weaker weapons.
There are A LOT of reasons why a ship can evade shoots forever, depends on the ship and the weapon involved ... the SR-2 Normandy did fine against the Collectors ship as its predecessor was destroyed.
It can evade shots forever? The Normandy SR-2 in a pitched battle against the drones, takes several hits, some quite serious. If you don't get Thanix you also take a serious hit from the Collector Cruiser.