Of course most B-26 combat was in the ETO. And in the book "Flying the B-26 Over Europe" the author, a navigator, explains why. They went to the RAF and asked for advice. The RAF told them that it took something like 5 min for the Germans to figure out the speed and direction of a flight of aircraft and lay an ambush box barrage. So if you are flying around Europe in daylight, you should change direction less than every 5 min and thus throw off the Germans' AAA targeting. USAAF Heavies could not do that and such ambushes were less effective against them anyway since they were 1 or 2 miles higher and larger guns were needed compared to the B-26's at 15,000 ft.
So the lower loss rate of the B-26 was very likely due to the rather extreme but effective tactics employed in the ETO. It seems that B-26's in the ETO almost never did low altitude work and strafing, despite those package guns on the side.
Postwar the B-26 was gone in a flash, and although the B-25 was no longer used as a bomber either, even before the end of WW2 it was being adopted as a multiengined trainer, where it had been found to be much less dangerous than the AT-9's, AT-11's and other small twins. The B-25 stayed on as a trainer and general hack transport for the USAF and ANG until at least 1955, with some photos showing there were still some left in 1965. They were also used for mosquito spraying.
