What if jobs and classes had specializations

[Tanathya]

Also, NIN was never meant to be a tank in FFXI (this is straight from the development team) - it was meant to be a fast-attacking debuff/DPS, until lazy players turned it into a tank by exploiting Utsusemi's Blink mechanic, and then complained when they inevitably were torn apart by enemies that ate through their shadows at once (being actually DPS they had all the defense of a wet paper bag). I'm glad FFXIV does not have any of that nonsense here.

So, this is about lazy players and not a good thing that the game doesn't fit you into whatever the game wants you in. Makes sense with that last sentence, you're glad FFXIV doesn't have it because you enjoy being shoehorned and not able to step outside the box, but damn it FFXI sure was open, whether you like it or not. It was actually clever of the playerbase to calculate the huge amount of volatile enmity a ninjutsu gave, and risk tanking with just Utsusemi and evasion. It was a high risk, high reward kind of tanking.

I dont know how that system worked in FFXI but I dont see it working here - and while I kinda hate to do this, I also feel the need somehow to point out something with threads like this that are clearly referencing FFXI: This is a differnt game. FFXIV works differently in an aweful lot of ways, so what worked their doesnt really work here.

In this case: Look how much of a hazzle it is with SMN and Scholar sharing the same base-class already. Altering the arcanist-skills is a balancing nightmare! And before they did away with our bonus-stats it was extremly annoying for people who were optimizig both jobs to actually do that, because those points were class-based, not job-based.

It would probably be a lot easier to release a ninja-like tank-class or a double-sword-dps than alter ninja and paladin.
To actually change what the classes are doing, a lot more than just switching out the weapon would be required.
A tank-ninja would need to gain more than just parry - he'd be mostly in need of skills that are generating aggro.
A paladin-dps wouldnt need only a second sword for looks but also an increase in skill-potency and the loss of aggro-generating abilities, not to mention some sort of replacment for all the now useless tank-cooldowns.
How does a bard healer work? Bards have zero skills to heal partymembers - they would need a whole new toolkit to fullfill that role, not only a harp instead of a bow.

And if you have to rework 50% (or more) of a job to make it work in a different role, arent you better off at that point creating a new, more original job from scratch?

I call "not thought through FFXI nostalgia" on this... which makes this a bad idea, sorry.

FFXI had nothing of the sort, so you made that up. Whether you could tank or not was mostly dependant on how the job was built and especially your subjob, nothing to do with the weapons.