Silly me, I forgot to include, "he wasted so much resource on stopping Allied shipping". Had Leningrad fallen, it would have been a terrible blow to Russian morale.
In his memoirs,
The Second World War, Volume 2, published in 1949, Winston Churchill confessed: ‘The only thing that ever really frightened me during the war was the U-boat peril.’
In 1939 Donitz expressed his belief that he could win the war with 300 vessels.
in 1945 Only 26 were in commission or under construction
From 1933 to 1936, the navy was granted only 13 percent of total armament expenditure
In 1935 shipyards produced 14 submarines, 21 in 1936, 1 in 1937. In 1938 nine were commissioned and in 1939 18 U-boats were built.
when the war started Dönitz had only 57 boats; of those, 27 were capable of reaching the Atlantic Ocean from their German bases. A small building program was already under way but the number of U-boats did not rise noticeably until the autumn of 1941
In May 1943, U-boat strength reached its peak, with 240 operational U-boats of which 118 were at sea,
[2] yet the sinking of Allied ships continued to decline. May 1943 also had the greatest losses suffered by U-boats up to that time, with 41 being destroyed in May 1943 — 25% of the operational U-boats.
[3]
by may 1943, The strategic advantage had been lost
had Donitz received his 300 u-boats in 1939, he might very well have starved Britain into surrender
that would have cut off the lifeline of tanks, planes & arms shipped to Russia & freed up a lot of German divisions to be deployed in the east
The Americans would not been able to fight a war in Europe & they would have focused on the pacific war
the result might have been different
A devils advocate could argue more u-boats would have meant less tanks / planes & thus a less effective blitzkrieg