I have played tanks since ARR. I will say Shadowbringers has made every tank feel the exact same.
You can point out these few minor differences like War AOE shield DRK AOE magic defense boost. The do different rotations like every damn class. Problem is they are all the same thing with a different effect and name.
From ARR to SB PLD had damage mitigation and support, while WAR had self healing and HP Buffs, and DRK had your magic damage mitigation as well as some self sustain and support. None of the classes played similarly with War being the power house DPS tank, DRK being your in between tank that works well for magic based fights, and PLD was your high mitigation, high support, low dps tank. WAR had a tank stance that increased its health and decreased its damage, and a dps stance that increased its damage and crit chance. PLD had a tank stance that mitigated damage and a dps stance that gave your auto attacks a double attack. DRK could use both DPS and tank stance at the same time. Each of these had moves there were only available during a certain stance as well. These were unique features of the classes but they were all able to tank equally in different ways. I still remember going in as PLD and healing A1S for anima farming with friends. When I look at GBR and think the only think different is a regen vs a heal and a extra rotation I can go through on CD compared to the above its laughable IMO.
Now the tanks do pretty much the same DPS, have the same cds (with different names or slightly altered effects) and have 0 unique flair. The only exception I would honestly make to this is the PLD with its magic ranged DPS rotation. The whole conversation here is not about gap closers its about each of the tank classes doing the same thing and not feeling like a unique class.
So you can decide if you prefer the cookie cutter model class with different colored flashes we currently have or if you prefer diverse options we previously had.