CD sharing of Vengeance, Nebula, Passage of Arms and Living Shadow, why?

[Rongway]

This post on another thread is generally along the lines of what I've seen offered before as an explanation whenever this question gets asked:

The cooldowns persist so that you while you're overworld questing you can't burn all your powerful instant attacks, change jobs away and back, and then burn all your powerful instant attacks again. So the cooldowns need to be kept track of even after you switch jobs.

But if the cooldowns weren't shared, then you could ostensibly burn all your instant attacks on RDM, then switch to DNC and burn all your cooldowns, then switch to NIN, then to .... etc.

It wouldn't happen very often, if at all, but the SE devs have always been at the extreme end of software design conservatism. They plan for the highest possible volume of data access and transfer, and the highest possible computational commitment, and take steps to minimize both, even when such extremes would be unlikely. Ergo limiting the number of cooldowns each player can have going at once by sharing them between jobs.

An addendum to my previous comment just to clarify: I used the example of blowing all your cooldowns on multiple jobs, but the recast sharing isn't about overworld balance or power; it's about how much memory your recast timers take up. If the timers weren't shared, you could blow all your cooldowns on every job, and end up using a hundred or more recast timers at once. Multiply this by the number of logged in characters and you have an obnoxious amount of memory devoted just to keeping track of recasts.

The real fun part is, sometimes the CDs don't even match. Like a 2 min CD on one Job could be a 90 sec on another, so if you use the 2 min one first, then swap to the second Job, you might see a 90 sec CD ability with more than 90 seconds to tick before it refreshes.

My favorite historical example of this was in ShB when Minor Arcana had a recast of 1s but it shared it with, among other Abilities, Blood Weapon, No Mercy, and Sneak Attack, so if you used any of those you would put an AST Ability on a recast 60 times longer than it was meant to have.