Sadly the submarine campaign against Japan would have been much mire effective without the issue with the US torpedoes. The Japanese were "helpful" in that ASW was never much of a priority for them, and they never had a decent convoy system. Of course, in addition to bringing supplies to the Home Islands, where proper convoy and escort would have been very helpful, they had a lot of far-flung garrisons to supply which meant a lot of unescorted sailings. As the USA reversed the tide and was taking islands, they had the shipping to have a smaller percentage of single ship sailings, and again here the Japanese doctrine helped. They saw submarines as fleet scouts and primarily to be used against warships, and never had much of an anti-merchant campaign. They had excellent long range submarines and torpedoes, and could have had subs sinking merchants off the US West Coast as well as attacking shipping to Hawaii, and the southern route to Australia, Samoa, Fiji, etc. Didn't happen.
Had the Japanese had an anti-shipping campaign, it would have forced the USN to produce more escorts, and possibly have diverted some forces from the Atlantic to the Pacific - not many, but still had convoys to Hawaii and Australia needed better protection... Japan still loses, but there would be butterflies.