Defense: 2 Carriers (6 Punch), 4 Fighters (16 Punch), 1 Battleship (4 Punch), 1 Transport (1 Punch), 1 Destroyer (3 Punch) Total Defensive Punch: 30 or roughly 5 hits in round 1 of a battle
Defense: 1 Carrier (3 Punch), 2 Fighters (8 Punch), 2 Battleships (8 Punch), 1 Transport (1 Punch), 1 Destroyer (3 Punch) Total Defensive Punch: 23 or just shy of 4 hits in round 1 of a battle.
Add to that number of units:
Scenario 1: 9 Units
Scenario 2: 7 Units
Add to that flexibility:
2 Battleship shore bombardments, 2 fighters
1 Battleship shore bombardment, 4 fighters
Honestly, give all three advantages for the two carriers and a fighter build (with consolidation of everything else in SZ 55) I think America is better off. After round 1 purchases I usually fall into battleship/transport/ground units in a KJF game. But the sheer advantage of starting off with the same number of carriers and being more flexible because of it vs having my units tied up in a central mass makes it better, in my opinion, to have the carriers.