The tonnages here show that even at 100% realism, the game still leans towards the Uboat (obviously since it is a game).
Total Decorations Awarded to Uboat force for duration of war.
Diamonds Winners (2)
Swords Winners (5)
Oak Leaves Winners (29)
Knights Cross Winners (144)
An ace was anyone with over 50,000 tons of kills and very few ever got past 200,000 for their entire careers so single patrols for 180,000+ were somewhat unlikely.
Early in the war you can pretty much sink ships with impunity since there aren't any escorts to speak of and you can just sit around on the convoy lines to pick off C2s and 3s and rack up some huge totals especially if you are selective and refuse to engage small ships (pretty sure that was a no-no for real captains ).
I think a better question to ask is with what mods since clearly operating under RuB and IC to eliminate all the fat single unguarded merchants changes the ability to sink large numbers a lot more than just difficulty since a lone C3 on 1% difficulty is just as easy to sink at 100%.