I know, but the reasons you cite (depth and maneuverability) clearly didn't work, or over 1000 u-boats would not have been sunk.
The edge would clearly go to the germans in the early war in terms of torpedo reliability. As for warhead, I think the torpex USN fish were about the same as the german types, if not more powerful. Stats on hits vs sinkings seem to bear this out (in another thread, I started by believing that german torps were more powerful, but looking at similar sized targets, the mk14s (and models with the same warhead) actually were more likely to sink various target sizes than even the late-war german torps.
That's based on the u-boat.net narratives for the ATO, and Alden's book on USN sub attacks for the PTO (match to japanese records). Note that the number of hits in Alden is if anything high since he lists
claimed hits, and I checked vs certain sinking or damaged results (based on the jap records). I checked 7k ships for both, etc, and a higher % of ships actually hit* with one USN torp sank than 1 german torp, even in 1944+.
*this is important obviously because early in the war they failed to hit/detonate enough that it made them look quite bad, indeed, and they were bad—except when they hit, when the torpex really did a good job
