This needs to stop !

[Poringing]

A lot of misconceptions regarding party dynamics found in this thread; let's clear this up:

Tank
Has near total control regarding maximum pace of the party, but very little control over minimum pace of the party.
The tank decides whether this will be a speed run or not, and how extreme the speed run is.
However, the tank's damage output is low, usually <1/6 a good party's total output.

Healer
Has most of the control regarding minimum pace of the party, and also some control over the maximum pace of the party.
If the healer does put out damage, this will be a fast run, regardless of the other party members. (Note: Since dungeons are designed with 0 healer damage output, healer's damage output is very significant when others aren't doing a lot of damage)
Also, a lot of content just cannot be done without a co-operative healer. On the other hand, a geared and experienced healer can cover for the tank for all 4-man content.

DPS
Has some control over both maximum and minumum pace of the party.
Even if both the attackers are very good at what they do, they are limited by the tank actually deciding to speed run or not; and if they are not that good, an attacking healer can sort of cover for them.

It's pretty obvious who has the most control over the party here: The healer. Seriously, they can hold the party hostage anytime. It will be completely impossible to do anything if there are no other casters in the party (BLM and SMN).

So, why are tanks given the role to lead the party? Respect. Simple as that. Everyone's answer to this thread can be boiled down to this, "Do you respect the tradition that dictates tanks lead?"

Personally:
I always run healer for low level roulettes: Control minimum pace.
While I always get into a party of 2 (preferably tank and healer) for high level roulettes. Fun fact: By running high level roulettes in a party of 2 (or 3), you have absolute control over the party (you want to /manderville for a full minute after every successful kill, you got it). Just fire the vote kick first and you'll definately have your way (in a group of 3, you can even torture all the people who joined in-progress). Pretty disturbing, huh?