As a rule of thumb, if you get the same sheet damage with a slower weapon, each cast of your spell will do much more damage for the same cost. And you probably can't sustain that or are forced to use generators, which would drop your effective dps. Ok, you can do twice as many attacks, so that's double damage. You do all your damage with a resource spender. With attack speed, it's often misleading because it does not account for your ability to attack at all. But sheet damage is missing more complex factors that might make all the difference. Ok so what I was talking about is this: Attack Speed is part of the damage hints.

These two factors are tricky to fully account for by just number crunching, in practice it just turns out that it's still superior anyways (resource is fine with LoV - Unstoppable Force and also gives 2x toughness with Crimson's, and Ivory Tower is really just apples and oranges hard to compare, but basically adds little to no value to the RG fight, and its utility for trash apparently doesn't redeem the loss in APS, or the build is too squishy to face-tank to get that value through blocks out of it anyways, I don't know, haven't played it myself, but it's not obvious). However, for HF it comes at a cost: Reduced resource efficiency, and missing out on Ivory Tower. Which again shifts the balance of power towards faster weapons (daggers), and among those Pig Sticker is the best again. It's just that APS is more important due to Shield of Fury, which effectively makes its DPS = DMG * APS 2 before it hits the cap and with BotS on RG after hitting the cap, too. Daggers and Pig Sticker win for the same reasons as with Invoker, but HF doesn't only care about APS, weapon damage does matter too. With Heaven's Fury it's a not as clear cut. Invoker just cares about APS so daggers win, and among daggers Pig Sticker wins because 5 primaries + dmg vs humans/beasts.

Diablo 3 wiki pig sticker