This would be incredibly OP even with half strength. FoF is 30% for 30 sec. Even if you cut in half both the power and the duration of it, it would be 15% for 15 sec for all party members. It would be twice as powerful as NIN's Trick Attack (50% more powerful and lasts 50% longer). Plus I think an ability called "Veil" should stay fully defensive. I think they should just increase the shield's potency (maybe to 15-20% of the Paladin's HP) and lower the CD to something along the lines of 90s.
As for raid DPS issues with a PLD, there is plenty of ways to fix that.
Hell, I hate suggestions. I always say that I prefer waiting for the dev team to show us what they got because they always do good things in terms of job balance (Look 2.0 WAR, MNK, DRG). But I also have some ideas that come in my head sometimes like "this thing should do this, why developpers didn't even think about it ?", so I'm gonna share a bit of that.
They could increase both threat multiplier and potency of RoH. Make it something like 280-290-300. Threat multiplier 5.5x like the other tanks. BAM. Now PLD doesn't lose as much DPS as now when doing his threat combo, and because he hits harder AND generates more threat with it, he can use Royal Authority a LOT more, thus increasing even more their MT DPS. Make Shield Swipe worth using (make it so that its potency is superior to the average potency-per-GCD of a PLD doing the optimal DPS GB-RA-RA-GB-RA-RA rotation). Do something to make Tempered Will useful for every fight in the game, something like, every spell casted during the duration of it can't be interrupted, and full immunity to all detrimental status effects, it would perfectly match the name AND fix the Clemency while MT issue. Make Clemency trigger Divine Veil but only in the case you're healing an ally and receiving the 50% portion for yourself. Reduce the cast time of Clemency to 2 or 2.5 sec to atleast match the GCD (like, seriously, why isn't it already the case ?). For the magical damage mitigation part, they could just make Bulwark give a 20% magical damage reduction on top of the already existing effect, because they said that shields will never be able to block magic (don't forget that Bulwark is 180sec CD, so this addition would be completely balanced and would never make PLD outperform DRK in the realm of magic mitigation). In the case of an only-magic enemy and OT-DPSing, make Sheltron do an additionnal effect in the case nothing has been blocked for the full duration, like, Shield Swipe proc when the debuff falls off naturally.
And because PLDs would get tools against magic, do something for DRK about physical too. Nothing too fancy, but just a little thingy to help. Like for example make Grit + DA only Souleater generate a barrier-type shield equal to the lifesteal we got with it (like an Adlo that shields for the amount of healing done) and make that shield work only on physical attacks. Active mitigation yo.
But all of that are just thoughts for myself, I'm confident that the developpers will bring balance to us and I don't care what way they'll chose, it may take more than 1 patch, but since 2.0 they always did a good work re-balancing jobs.