I think the number of bomb hits was much higher, but misleading. The strike was thrown together quickly and two factors made the bombing very ineffective. First, most of the aircraft launched without AP bombs, second a very low cloud cover that day made dive bombing impossible.
Normally, it took an AP bomb dropped from above 3500 feet to penetrate a battleships top armor.
As far as the Yamato and Mushashi are concerned:
Both were sunk while operating without air cover and bad ASW defenses. What defenses there were were simply swamped.
The Mushashi, if memeory serves, took 19 torpedos and 17bombs before she sank. The Yamato took similar damage and had even less of an escort.
The Yamato and Mushashi were extremely slow vessels for their day, capable of only about 26 knots. An Iowa class ship could make 33 knots.
Had Iowa and Yamato class ships slugged it out in WWII, the Iowas would have come out on top -- they were faster, had better armor and the rifled 16" gun was more accurate, and had similar range the Japanese 18" gun (I believe the difference was merely 2,000 yds or so).
In a stand-up slugfest, the Japanese would have been deficient in radar and fire control. The gun crews would also have worn out faster than the Americans because of the more intensive labor involved in slinging 18" shells.
Comparing the Yamato to the Iowas is a BAD way to try and make your point. The ships were constructed differently and for different reasons --the Japanese putting a premium on size and symbolism, the Americans on accurate firepower and survivability.
A better comparison to the Iowas would actually have been the Bismark and Tirpitz. A surface battle between these ships would have been a much more fair fight, although we probably still would have won.