And I'll have to step in and remind you that class stacking is very much SE's fault, between class/job design, ability and damage spread between jobs, and encounter design and balancing (or lack thereof). Pacing of content has had a hand in it, and of course speed runs never helped. Sure, you don't care because you run with a shell, but many of us PuG things, and it's not all sunshine and rainbows; not to say it should be the prime way of doing content, but it should also not be the uphill battle it currently is.
Game mechanics influence the way the playerbase does things. This is why the community was so self-mutilating in FFXI as far as player choices went, and you insta-sucked if you went against the grain.
As I've mentioned in other threads, class stacking should occur as freak occurrences that generate laughs while making the dungeon run interesting and doable, and a varied and balanced group comp should be the way most if not all groups aim to do content. XIV has a LONG way to go before that becomes a reality.
PS: As far as the mentioning of how long it takes, the deciding factor should be how your DPSers perform. The tank should not be a factor in that equation at all. It shouldn't matter if the tank is a WAR or PLD or SAM or BST or whatever; the result should be the same. If a run takes longer with a PLD and shorter with a WAR, then there's a balance problem and in needs to be resolved.