The biggest determining factors for WAR DPS comes down to 4 things. When I compare parses these are the key things that I look at when trying to improve.
The first and biggest influence on WAR DPS is Deliverance up-time. You want to be in Deliverance as much as possible. You should be relying on your dCDs for mitigation and Defiance as a last option. If you use Defiance, you want to pair it with Unchained to negate the DPS penalty so that it functions more like ToB + Conva.
The second is general up-time. Lost GCDs are a big hit to your DPS so your goal is to maximize up-time. Up-time optimization is fight specific -- in a fight like Sephirot, there is some nuance to this like lost GCDs during p1 movement for re-positioning and green / purple, timing pacification to correspond with orange if you are not using green stacking for melee, add management, etc. Look at a top parse and compare their aDPS up-time to yours. You should rarely need to Tomahawk to deal with down-time.
The third is your stack management. Find a comparable clear-time parse with better DPS and look at how many FC / IB / Decimate / Steel Cyclone uses they are getting. If you are lower, chances are you are holding stacks or messing something else up. You ideally want to use stacks with close to 100% efficiency.
The fourth is your buff management. The biggest contributing aspect of buff management is your Berserk up-time. For Sephirot EX, you can use 2 full 9GCD Berserks every p3 cycle on the same rotation but most WARs mess this up. An earlier poster gave the advice to hold Berserk for small phases in A5S. This is bad advice because you will lose a Berserk unless your party has a specific clear time. Even a gimped Berserk is better than no Berserk. When judging a fight, pay attention to the duration of phases, the timing of down-time and maximize your Berserk uses. There are some exceptions to this like Hummel (where there is an actual downside to getting 2 Berserks vs. 1) but generally you want to keep Berserk as close to off CD as possible while not sacrificing its up-time or buff synergy (using it on 4-5 stacks with Infuriate or syncing with buffs like Balance, IR, TA, BL, etc.).