The issue as I see it stems from a lack of useful tanking stats. If tanks were forced to have "proper" stats, and as mentioned by someone earlier in the thread, bosses were virtually (or actually) untankable outside of tanking stance we wouldn't have the same issue as to whether tanks should be in VIT accessories or STR (which they can't roll on but do need at present).
I would agree with the earlier poster that there needs to be a shift to really change the focus on each role doing what they are designed to do. Tanks should be the only ones, in my opinion, who can stand in front of the boss, take a hit and not get dangerously low on health (notwithstanding attacks like blinding blade needing to be shared).
My suggestion in another thread was three specific tanking stats - Parry, Evasion and Resistance (general damage reduction and healing received increase). It would need a significant re-work of the tanking setup, and thus is very unlikely to ever happen, but I can dream. Each would have different scaling to differentiate the tanks - DRK for instance would want Parry to a soft cap and resistance, with the design being they mitigate many attacks, but have reasonable defence against ones which get through, WAR would go for Evasion, avoiding attacks as much as possible, but having a large HP pool and naturally increased healing from their stance to recover when they do get hit and PLD would go all out Resistance, minimising the amount of damage taken (per the idea that they are there as the defensive tank), but taking more hits as they would have low parry/evasion stats.
Couple this with overall increased single target damage from bosses (I would say an unmitigated auto attack be around 8,000) and increased damage reduction from tank stances (go to 40% and add 20% to WAR stance to make it viable on top of the healing+ it already has) it would mean that tanks needed to be tanks, not quasi-dps. Secondary stats would then mean that the overall damage was reduced to around 3,000 average per hit for a tank, or (with increased HP due to VIT stacking) approximately 1/6 of their total HP pool.
Like I said elsewhere, this is from an experienced MMO player, but not necessarily experienced FFXIV.
Edit: Alternatively, just make vitality worth something other than HP. If tank abilities scaled off it that would work, but perhaps instead think outside the box (and drive tanks away from this DPS>>>>>>everything thought process) to have it add passive damage resist, perhaps in the region of 1 point VIT = 0.01% damage resist. That would allow tanks with the current gear up to about 10% damage resist I think. That would allow healers to DPS more (to make up for the lack of extra tank dps) if required and would make VIT accessories desirable for tanks.