Hmmm...to my knowledge, the daylight bombing only started after the P-51s entered the fray because they could cover the higher flyers. The Brits did their thing at night because they were better versed on the terrain and the US had issues navigating at night from a foreign land!
Daylight bombing started in 1942 before there was the P-51. The air crew losses were atrocious , 50% casualty rate for the war. There were as many lost in training accidents in the states as in the war.