Just to be clear, I never claimed it was a waste. I claimed that as a WAR, you feel really bad needing to use IB because of how big of a DPS hit it is. And, in relation to FC, that it is a trade off.
So, as you've detailed, you are indeed losing something when you FC. Yes, you gain something, too. But that is literally the definition of a trade-off.
Obviously. I don't think you really need ShO to survive anything anymore but my point was more that you frequently don't need to expend the GCD switching back to SwO or to SwO initially.
When you IB instead of FC, this is what you give up --
630 potency with at 10% crit boost. I think the current crit multiplier for BiS gear is around 170%. I think on average, that works out to around 674 potency.
So you lose 314 potential potency on average each time you IB. After that, you are stuck in Defiance for another 4 GCDs. Assuming the best case scenario where those 4 GCDs are HS, Maim, Path, and HS, it breaks down like this: 135+171+225+135. If you were in Deliverance, those potencies would be 189+239.4+315+189 with a small amount of average potency added based on crit. That totals out to another 266.4+ lost potency.
As for PLD, whether or not the potency loss is worse depends entirely on what GCD is being pushed out of the phase/fight. Just to do the hypothetical math -- assuming you swap to ShO after refreshing GB, lose an FB and SB at the end of the fight due to Oaths consuming 2 GCDs, have a 2.24s delay weapon, and spend 2 GCDs in ShO to weather the tank buster, you lose ~150 potency from lost SwO bonuses (potentially only 100), 150 + 200 potency from the lost FB and SB, and 22.5+30 from the ShO damage penalty on your FB and SB while in ShO. That totals to 552.5 lost potency + some potency lost from GB clipping. If you are getting anything else but FB and SB pushed out of the phase/fight then the loss is larger.
If its just a one way swap to ShO / Defiance, the PLD loses less potency because their subsequent potency loss is lighter.
Assuming an Eye > BB rotation, WAR's ppGCD in Deliverance is ~344+ including Maim and FC but not including the Deliverance crit bonus. Their ppGCD in Defiance is ~234 including Maim and IB. PLD's ppGCD in SwO is around ~320 not including the things I specified earlier. PLD's ppGCD in ShO is around ~229.
But this is actually not really relevant. My point was that WAR has to trade DPS for mitigation. I think the numbers clearly prove that. I never argued it was more or less than PLD.