If I had to take a guess, it's the combined 12 DEX and the fact that even one extra hit before a Rudra's (more tp) makes that big of a difference in damage, because of how well Rudra's scales from 1000-2000 tp.
But somebody else who is more mathematically inclined would have to give you a more concrete answer.
I can tell you for sure that the reason Sushi/Delve Fodder set wins over Acc/RCB sets (that I've tried anyways), is any single STP you take off in place of acc drops your dps by a large amount. STP is absolutely fucking broken for THF atm because of Rudra's scaling.