Due to how each DpS class synergizes with the other DpS classes there are multiple viable dps raid party compositions, pretty much every dps job is in multiple of them and no one job is in all of them. One of the problems that tanks have is that only Warrior is viable in each and every tank composition it is in. Warrior + Dark Knight is optimal, Warrior + Paladin is viable, Dark Knight + Paladin is not viable because of lack of the Slash resist debuff from Storm's Eye or Dancing Edge. Sure you could have a Ninja be one of the dps in a Dark Knight + Paladin comp, but Warrior + Dark Knight/Paladin + Ninja is more optimal.
So unless there is a way for the Dark Knight/Paladin comp to get the Slashing debuff without the whole comp being more optimal by replacing either tank with a Warrior, adding a 4th tank will not fix the problems that give Warrior a guaranteed raid slot.
Deployment Tactics is what makes Scholar shields stronger than Noct shields. A Noct Astro can't completely nullify most of the raid wide damage in the first 20 seconds of the fight by throwing out a 390 to 1296 potency shield at the start of the fight. The rest of the two jobs kits are pretty comparable with the scholar's dps being roughly equal to the party dps increase from the Astro's cards.This isn't the only reason SCH is so viable.. the noct AST shields are actually stronger then SCH shields if not crited. Its all the utilty it brings, being able to spread a single target shield onto the whole party + burst heals + pet healer + highly sustained DPS while keeping HPS up.
If the Storm's Eye/Dancing Edge debuff is not factored in Warrior Dark Knight and Paladin dps are pretty close together now. The Storm's Eye/Dancing Edge debuff increases all three tanks damage by about 10%Its the same for WAR. WAR isn't only viable for its 2 debuffs or DPS, its actually very close to DRK DPS. What WAR does great is its self sustain on top of all its utility, having one of the most on demand mitigation skills in the game on top of its ability synergy.
Applying the same debuffs does not make to jobs the same. If the Samurai used combos to generate stacks and then used those stacks to perform special attack they would be similar.Your literally describing WAR as a DPS. Also 2 DPS? This is shooting the tank population in the foot.
Also I never said that they should only release SAM and RDM together or released without any other classes (one of which could be a tank) I only said I'd rather see the Samurai as a DpS that would be more viable in non-Warrior comps and added that I'd like Red Mages to use bucklers.