One B-17 could carry 8 times the explosive load of a V-2, and a Lancaster could carry 17 times as much. The HE 111 was not a strategic bomber, and half again as much bang as a V-2. The lack of a true, good ol' 4 piston engined strategic bomber was an almost incaluable mistake by the Germans. Surely they could have built a fine one. They invented strategic bombing, and had huge bombers in WW I, but they built a lot of weird stuff instead.

U-boats were absolutely getting crushed in 1945, by the way. Their harbors in France were surrounded, the Lutwaffe was gone, and the Allied navies had their number.