in b26s you would have needed almost all of your bombs to hit, and make sure that you were using the heavy load. you may well have killed loads of guns, but i think the flak that kept shooting you was the stuff from the cruiser (there is ack over all of the boats, not just the CV).
in regards to shooting the guy down, you have to concentrate your 50 cals intoa certain spot to do a large amount of damage. i expect he flew off because you wounded his pilot or shot some important control surfaces off
you just need a bit more practise, and a bit more luck mate