Bombers add counterattack but they don’t sit on the seazone and so they don’t defend you (except in the sense that they threaten whatever japan has left once its your turn).
In 42.2 (and 42.3) unless you kill Japan’s Java Fleet or it makes some serious money mistakes, it can build against you 1:1. This means that if you buy subs or bombers (or other junk like transports that do nothing to protect your fleet in place) japan will have more hits on both offense and defense (its usually about 14 Japan Naval hits to 16-17 USA and allied hits if the allies play super-optimally) when we are talking about a face to face confrontation in a classic naval battle.
The USA is just really hampered here; in 42.3 they need to spend 100% atlantic to even try the KGF. In 42.2, they can buy optimally (bbs, dd, carriers and every fighter) and still only match, not beat Japan.
Many times whether the USA steps up on defense or it uses the bombers etc to attack, they lose it all during that fairly even battle and then Japan can do whatever it likes. this makes KJF even more suspect, in these editions.
