After flying both a lot the Zero is just better.
The biggest issue is gun convergence or lack of gun convergence on the Corsairs. The Zeros inline mgs are far superior then the wing mounted on the Corsair. Do to the lack of convergance on the Corsair. One of the wing mounted guns will miss most of the time while one hits vs the Zero where both hit consistently. The Zeros ablity to put both barrels worth of damage in the same section of the enemy resulting in much better and consistent damage.
This issue is most telling on the F4-A1 vs the A6M2.
The second issue is the A6M2 tech tree. The 3rd unlock greatly favors the A6M2. Finned barrels + the advantage on inline mgs make it the clear winner vs the Corsair bubble canopy and wing mounted mgs. Bubble canopy is worthless but you have to take it to get ground attack cannons and incendiary bombs. Unless there is a forced cockpit game mode the bubble canopy is just a waste vs finned barrels.
I noticed I shot down Corsairs twice as fast in my Zero vs the Corsair downing Zeros. Talking strictly time to kill here.
If anything the finned barrels should be a Corsair unlock as it needs the extra firing time to make up for the poor performance of the wing mgs vs the Zeros inline mgs. Or they need away to set the convergence range on the Corsair guns.
Now before someone says in real life blahs blah blah. I'm strictly looking at game balance. In real life Zero had a slim chance of beating a Corsair as the Corsair was faster, climb higher and better armored. Japanese would need something like a N1k to compete. This is game play I'm talking about and the Corsair F4U-A1 is at a distinct disadvantage imo.