Are people still claiming that WAR is at some sort of a defensive disadvantage? In what content?
If we're talking prog/early content clears, WAR tends to be (perhaps surprisingly) the best tank defensively. That's because defensive stances (and IB) actually do get used in brand new fights before mechanics are known and fight guides/timestamps get mapped out. The safest bet in blind prog is probably to use a WAR with PLD support, unless you can be certain that you're going to be getting a lot of value out of DM). If we're talking farm content, there isn't really anything that can't be solved with Holmgang and Vengeance, so WAR is no slouch there either. If you feel forced to use IB/Defiance in farm, then the problem isn't the job.
"Utility" is a meaningless buzzword. If you're using it to refer to raidwide mitigation, WAR has the edge because of Shake it Off. But it's not just the defensive value of Shake and Veil that make them powerful. It's the large amounts of LB that they can generate from shielding critical raidwide damage, which in turn shaves down fight-time when you plan for their usage well.
If you're using "utility" to refer to Cover, then yes, PLD can do some interesting things every so often with it, either in how it interacts with boss abilities (the old Earthshaker trick) or by letting someone else do a mechanic for you and taking the damage on their behalf (like the enmity resets in O4S part 2). But these are just alternate solutions that provide PLD with a bit of extra convenience. You can still work around not having it.
It's not utility that you want. "Utility" was a pretence. The reason why WAR mains brought up "utility" pre-4.2 was because they wanted to be uncontested at dps. "If we lack 'utility' (vague term) then you must give us dps to compensate," they insisted. They got both, even though they didn't really care all that much about the former.
The problem to date is that we've placed tanks on this spectrum. PLD is the "defensive tank". WAR is the "offensive tank". DRK sits somewhere in-between. Every tank needs to be able to clear content, so there's never really a situation in which a tank is at a true "defensive" disadvantage. You're not being forced into tank stance on WAR in farm content (if you are, perhaps you need to re-evaluate what you're doing). But if another tank starts to shine offensively, there are riots.
I think this is where Gunbreaker needs to come in. Rather than having this spectrum, you have four separate tanks, each with their own strengths and weaknesses. No tank dominates offensively or defensively. We break down these privileged positions like "best offensive tank" for good, and replace them with actual niches.
I'm not really sure what the best niche for Gunbreaker would be, but after watching the trailer, I want them to be extremely mobile, and to see fights that let them take advantage of that.