Exactly.
Before America came into the war the German subs had the potential to go a long way to isolating Britain from its sources of supply. After America came in a bigger German sub fleet could still have hampered trans-Atlantic supply and, perhaps more critically in the early years of American involvement in the war, severely reduced supply to the USSR. Churchill said that the thing that worried him most in WWII was the U boat threat in the North Atlantic, and he was in the best position to judge.
Even if that happened, how would it have affected the critical issue of transporting supplies across the North Atlantic to Britain and to the USSR?
Germany could have had several fleets of jet powered fighters and even jet powered bombers, but they still wouldn’t have reduced the trans-Atlantic LOC which were fundamental to creating and or maintaining the Allied offensive against Germany which, before and for that matter on D Day, relied primarily on sea power and transport.
Any aircraft Germany developed after 1940 were, realistically, capable only of delaying its defeat rather than altering the course of the war. That wasn’t necessarily the case with investing in submarines.
