Historically that's not the case... Many examples of cruisers and such being strafed down. It's not that you're punching holes in the water line, it's that you're hitting other vital areas. Some dramatic gun cam footage out there of several ships' boilers blowing up from strafing runs.
Now, the big flaw in most US carriers was the weak deck armor. Often times bombs went right through it. It was for the aircraft, not for the benefit of the areas below it.
Now there's a completely different debate as to whether CVs could be strafed down and sunk by gunfire only, but historically warships were killed with 50cals.
Buttloads of 50cals mind you, but 50cals nonetheless.
EDIT: Note that in AH this may or may not apply. Right below the CV deck was storage, gas, bombs, the giant hangar bay where all the planes were prepped... A fire in this area usually resulted in out-of-control blazes that eventually sunk the ship. Is it going to end-up like AH's damage model shows? No... But it'd be out of combat. Debate is open as to whether it's valid in FSO and whatnot.
There was no evidence of any US warship that was strafed and sank that I am aware of. You saw footage of foreign ships being strafed but not a US warship causing it to sink. If so provide it, I am aware of none. Frigates, Destroyers,,,, maybe. Never happened to a CV or a Battleship/Cruiser.
As what has been stated, .50 cal loaded with AP (armor piercing)would still not be able to penetrate the hull or even the hanger deck of a CV.
"armor-piercing" was required to completely perforate 0.875" (22.2 mm) of hardened steel armor plate at a distance of 100 yards (91 m), and 0.75" (19 mm) at 547 yards (500 m).
Essex class fleet aircraft carriers
Displacement: 34,881 tons full load
Dimensions: 820 x 93 x 28.5 feet/250 x 28.3 x 8.7 meters
Extreme Dimensions: 872 x 147.5 x 28.5 feet/265.8 x 45 x 8.7 meters ("Long Hull" types: 888 x 147.5 x 28.5 feet/270.6 x 45 x 8.7 meters)
Propulsion: Steam turbines, 8 565 psi boilers, 4 shafts, 150,000 shp, 33 kts
Crew: 2,631
Armor: 1.5 inch hangar deck, 2.5-4 inch belt
Armament: 4 dual, 4 single 5/38 DP, 18 quad 40 mm AA, 61 single 20 mm AA ; single 20 mm AA replaced late WWII/postwar by 35 dual 20 mm AA
Aircraft: 100
And for the record, The "cruiser" in this game is modeled much like a Battleship and looks more like one. Either way, they were both heavily armored, their weakness was the stacks, which if even a small amount of ords was dropped into the stack area would disrupt the boiler causing a massive explosion.
Whether .50 cal bullets can pierce the hull is not relevant. Imagine a ship that has been hit with 10+ 500lb bombs. There would be hull damage, fires and all kinds of secondary damage going on. The ship's crew would be working franticly to contain the damage and keep the boat afloat. If these crew members are not able to attend to the ship because they are under fire from straffing aircraft or killed by them, then the ship will perish as Vulcan has already stated. The simulation of killing these crew members or doing other damage to the ship that causes secondary explosions as Krusty has mentioned, is why .50 cals are allowed to do damage to ships in the game. It is not out of line with what historically happened. It would help if you were to expand your perception to include these kinds of events when considering the damage of straffing aircraft on ships.
Your way off and its way out of line of what really happened......... Ask the Chief Shipmate...... You do realize that the ship under attack in your scenario would have all hands below deck complelty safe from strafing with .50 cal. We call that GQ(General Qaurters) the only people topside in WWII would have been the gunners manning all the flak guns and various gun mounts. The other 2,000 Sailors would be below deck. Sure there would be secondary explosions, fire, etc. but if we are going to account for all of that then shouldnt we expand our perception to include these kinds of events as the ack from the battle group? 18 fighters came in and not one was hit with ack that destroyed their plane. Where do we draw that line of make-believe?
It wasn't just sunk with 50 cal weapons, it was also sunk with bombs.