Fix paladin. Only Class in the entire game that cannot...

[Reynhart]

And the self-healing tank should be PLD.
You know, the job that is defined by "A fighter that can heal"...

[Jandor]

In an ideal world the Dark Knight would bring debuffs and up the DPS that way, the Paladin would bring party buffs and up the DPS that way and the Warrior would bring a big axe and hit things very hard upping the DPS that way.

Giving each tank a main thing and a secondary thing and then trying to stop them to stepping over each other in those areas would go along way.

WAR: 1. Big numbers 2. Reliable cooldowns
DRK: 1. Potent debuffs 2. AoE monster
PLD: 1. Potent buffs 2. Very good straightforward cooldowns

At the moment though, it seems WAR is at least adequate in all those areas, great in a lot of them. It doesn't leave much room for the others IMHO.