Why use a Dragoon or Monk when you can use a Warrior?

[Frein]

WAR in tanking gear = high VIT and HP, the cost of that is low STR, Crit att power/rate, att power etc,

You forget that WAR actually gains damage from VIT the same way MNK gains damage from INT and DRG gains damage from PIE. The fact that WAR can stack one stat and one stat only to cover just about all angles of their gameplay to a great degree (STR is still more effective for damage) gives them a fundamental edge over other classes that rely on multiple stats, like PLD who needs STR to block (despite SE insisting DEX affects this), VIT to gain HP and absorb damage and MND to cure (and for damage).

I was about to "fix" it by saying "people in GENERAL" but then that would be a bit too much as far as negativism go.

How ironic that you'd post this after writing a lengthy post about how running an inferior and less specialized group setup is better because it, somehow, lets the players complement each other more. In the end you manage to answer your own question, though: It's easier that way. It just makes no sense to do something the hard way unless challenge is all you're looking for.