Carbonx has a good point.
Threat and Damage are interlinked but in an annoyingly exponential way. For Paladins and Dark Knights, the threat combo they have (Halone or Power Slash) is the lowest potency combo, so they ideally want to do it as little as possible to max their DPS. Dark Knights have more potency and threat on theirs, so a Dark Knight might need to only open with a single power slash combo, a PLD might need to do two halones before they're comfy with a lead (depending on if you have a ninja, party dps etc).
The more DPS you do, the more inherant threat you put out and thus the less you need to rely on threat combos. You only need to do as much threat as 1 greater than the highest threat DPS in the raid, and Bonus Enmity only exists as a way to shore up the difference between your -actual- dps and their actual dps. The more dps you do, the less you need to rely on bonus enmity moves/stances to keep yourself above the dpsers.
Paladins do slightly less DPS when tanking than the other two classes, and thus need to use their threat combo slightly more on average. Their threat combo is also weaker, lower potency, lower threat and has a proportionally much bigger potency loss compared to other tanks when they could have done a Royal Authority combo instead (a PLD loses 80 potency when forced to do a Halone instead of a Royal. A DRK loses 10 potency when forced to do a Power Slash instead of a Delirium. In contrast a Warrior's Butcher combo is 20 potency more than their Storms Eye).
In contrast, not only does the Warrior do more damage naturally, but the Warrior's threat rotation (Butchers) is actually their highest potency combo and thus they WANT to do it lots. The Alternating Eye/Butchers combo means that when doing their max dps rotation they're also putting out far more threat than a Paladin doing Goring/Royal/Royal.
This is part of why there's such a big gap between dps values in practise. It's not that Paladins and Dark Knights have trouble holding threat, they don't. It's just in order to -really- minmax their DPS they sacrifice far more threat than a Warrior would. The optimal paladin rotation for dps is Goring/Royal/Royal whilst in Sword Oath, and this will NEVER hold threat off a well geared DPS doing their maximum rotation without either a.) a Ninja for threat transfer or b.) a comfortable threat lead. By reducing the requirements for that comfortable threat lead, you're technically pushing up the potential DPS ceiling for PLDs and DRKs, and bringing them a little closer to WARs.
Imagine if Royal Authority had a 5.5x enmity modifier. Halone would never be used other than as a mitigation tool to apply Str down. Paladins would be able to open pulls in Sword Oath even without a ninja, and never lose threat to anything whilst doing their max dps rotation. I'm not sure this is necessarily what we want as it takes away the skill of playing the class a bit, but it does highlight how increasing threat values can potentially increase their practical MT dps significantly.