raid mechanics will always dictate party comp. No skill is useless but the content in which they are put in makes them so. SiO is a great idea in execution, a self esuna and even worked on things like doom in exdeath but content was created so you couldn't ignore such debuffs and thus made SiO useless and changes were made. Assuming we are getting a fourth tank in 5.0 they need to either start pairing tanks, ex WAR/DRK and PLD/TANK, where they would complement each other much better than they would with another tank or make sure that each tank has a baseline. Things like a party shield, self-heal action/ability and offensive cd, for example, each tank would have its version but with different approaches to achieving said results.

I feel that they need to stick to the lore of the job and work around that. That is the only way to make jobs feel different while still being homogenized. PLD has always been the shield of the party protecting others and have skills like PoA and Cover. WAR is a berserk, beast that you had to harness and control and have skills like IR and FC. DRK has always been about inner conflict and eternal struggle with a focus on life-steal and have skills like Blood Weapon and TBN. I feel like all three tanks achieved this in 4.0 though DRK definitely got the short end.