If Holmgang is 6m...

Then it just means that the new FotM will be Gunbreaker because 5m CD on Superbolide (Same as DRK, but DRK requires more co-ordination to fully utilize, while GNB you just pop it and have 8 seconds where healers can heal you up no problem and even if you get insta-Benediction'd you still retain the rest of the duration being immortal)

Since, WAR's dominance is mostly centred around Holmgang's reusability vs other Tanks (3m vs 5m/7m).

With the secondary concern being DPS - Notably how much being consolidated into their burst window (To stack with Trick Attack and other rDPS CD's) alleviates boss downtime as opposed to statistically superior overall DPS. But with other Tanks becoming burstier too (PLD getting Confiteur as well as having Atonement spam during FoF and DRK getting Inner Delirium) as well as rDPS CD's being reduced across the board, this should be mitigated.

Just an observation. WAR will still be fine. But its presence as "Dominant Tank" will just be passed on to Paladin and whatever out of DRK/GNB will end up being second best Tank. (At least, until 5.1 thanks to those anti-WAR posters who keep bumping up every Tank thread to talk about WAR )