Thought on GNB's mitigation overall

[mosaicex]

You guys really can't evaluate tank's mitigation skills in Vacuum, you need to compare them to what other tanks have.

First off, they all have passive Mitigation/Restoration: Blocking, Storm's Path, Souleater, and Brutal Shell
Then they all have Rampart and Sentinel's equivalence (with WAR's being juuust slightly better)
They all also have spot mitigation skills: Sheltron (19%-20%), Raw Intuition(20%), The Blackest Night(25% of DRK's max HP), and Heart of Stone (15%)
They all also have spot support mitigation skills: Intervene(10-25%), Nascent Flash(10% + heal from WAR), The Blackest Night, and Heast of Stone (15% + 150 potency Shield)

After that came teamwide mitigation: Divine Veil (10% of PLD's max hp, probably the strongest tank's teamwide mitigation, at the cost of requiring GCD heal to proc + Passage of Arm (requires good positioning for spot use)), Shake It Off (8%-20% of receiver's max HP), and then Dark Missionary and Heart of Light (both 10% magic mitigation)

And of course, a heal: Clemency (requires a GCD, won't see usage in most case), Equilibrium (1200 potency self-heal), Abyssal Drain (200 potency per target, extremely strong in big pull), Aurora (1200 potency total regen, can be used on self or target)

Then super cooldown, but I'm not gonna go deep into this subject because in controlled situation (namely EX trials and Savage raids) they are all pretty much equally strong and their limitation is solely on the length of the cooldown (and duration, in Holmgang's case)

Finally, they all have 'extra' mitigation skills: Cover, Thrill of Battle, Dark Mind, and Camouflage.
Cover, as the name suggested, lets you take damage, but without innate damage mitigation, its use is solely for mechanic cheesing (that I haven't found any yet in 5.0 content since it doesn't work against Fae Light in Titania EX)
Thrill of Battle, for all intent and purpose, is 20% max HP heal for WAR since the additionally hp recovery only works with GCD heal, something healers don't want to overdo
Dark Mind, a 20% mitigation, except it only works on magic attack.
Then finally, Camouflage, 10% all type damage mitigation and 50% parry.

So I want to ask again, what exactly is Gunbreaker lacking compared to other tanks?

[Kaozurei]

First off, they all have passive Mitigation/Restoration: Blocking, Storm's Path, Souleater, and Brutal Shell
I concede this point, though PLD's blocking is pretty noticeable mitigation.

They all also have spot mitigation skills: Sheltron (19%-20%), Raw Intuition(20%), The Blackest Night(25% of DRK's max HP), and Heart of Stone (15%)
5% damage reduction does make a difference, especially when being used to mitigate tankbusters. No reason HoS should just be a worse RI.

They all also have spot support mitigation skills: Intervene(10-25%), Nascent Flash(10% + heal from WAR), The Blackest Night, and Heast of Stone (15% + 150 potency Shield)
The 150 potency shield from Brutal Shell barely adds anything meaningful to Heart of Stone when used on the MT, it'll break in a single hit regardless without mitigating much unlike TBN or Intervention.

After that came teamwide mitigation: Divine Veil (10% of PLD's max hp, probably the strongest tank's teamwide mitigation, at the cost of requiring GCD heal to proc + Passage of Arm (requires good positioning for spot use)), Shake It Off (8%-20% of receiver's max HP), and then Dark Missionary and Heart of Light (both 10% magic mitigation)
Not every fight has raidwide magic damage to mitigate. Dark Missionary and Heart of Light are completely useless in these situations. Mitigation counts for dungeons too.

And of course, a heal: Clemency (requires a GCD, won't see usage in most case), Equilibrium (1200 potency self-heal), Abyssal Drain (200 potency per target, extremely strong in big pull), Aurora (1200 potency total regen, can be used on self or target)
Clemency can be spammed in an emergency for as long as MP allows. Equilibirum is a really powerful self heal and Abyssal Drain is really powerful in large pulls. Aurora is a HoT, making it unreliable as emergency healing and only really serves as a tiny bit of mitigation mid-pull.

Finally, they all have 'extra' mitigation skills: Cover, Thrill of Battle, Dark Mind, and Camouflage.
Cover, as the name suggested, lets you take damage, but without innate damage mitigation, its use is solely for mechanic cheesing (that I haven't found any yet in 5.0 content since it doesn't work against Fae Light in Titania EX)
Thrill of Battle, for all intent and purpose, is 20% max HP heal for WAR since the additionally hp recovery only works with GCD heal, something healers don't want to overdo
Dark Mind, a 20% mitigation, except it only works on magic attack.
Then finally, Camouflage, 10% all type damage mitigation and 50% parry.
I admit Cover is worse than anything the other tanks have in this regard, so I concede this point as well.

Added my replies in bold, though I took out some points (Shared 20/30 cooldowns and invulns) as I actually fully agree with those. Honestly, if Heart of Stone was 20% mitigation, at least when used on self, Heart of Light was changed to mitigate all types of damage and if Brutal Shell's shield were stronger then I'd be pretty happy with GNB mitigation as a whole. I'd even take superbolide's lovely heal GCD wasting risk.