The reason why niches are bad was already exemplified in A1S-A4S and is a basic idea within class design in any multi-class game. PLD's first A4S was 4+ weeks after the first DRK / WAR groups. Why? Because PLD was niche in that it was the only low DPS, low magic-mitigation tank. Because we had niche tanks, they reacted differently to the same content and PLDs lost out.

Nobody thinks it was a good idea to have one tank incapable of doing content without 4 more weeks of gearing. The mass exodus from PLD is proof of this.

So, why are we discussing the idea of going "one step beyond" in relation to PLD's supposed defensive niche? So that PLD can clear content 4 weeks ahead of WAR and DRK while they wait for gear to push them over a specific eHP threshold? One step beyond is giving PLD a meaningful advantage in eHP -- an equivalent advantage to the higher DPS of WAR and DRK. We've seen what that means already.

It was bad design when it was DPS. It's still bad design when it applies to mitigation.

They admitted to their mistakes in tuning. Why are we suggesting they should repeat those mistakes in another way?

All tanks need to be able to survive content. The moment a tank is incapable of surviving content, they are no longer a tank. They are nothing. So, you set the baseline at the lowest survivability tank. But, by doing so, you are just falling back into the current meta where anything over that baseline is sacrificed for more DPS.

And, if all you cared about was casual content, then none of this discussion needs to happen. They could make PLD even worse and they'd still clear the next Alex normal just fine.