I dun play paladin but was having an idea of

Warrior = offensive tank (High Hp, High attack)
Paladin = defensive tank (High block rate, High defense)

Correct me if Im wrong but the tank's main job is to keep the mob on them right?
So getting and maintaining enmity is the primary purpose of the tank.

Warrior generate enmity by doing more damage,
Paladin could increase enmity by a partial or successful block.

Warrior should need more heals in a party when tanking
Paladin should require less heals (excluding that he heals himself)

This should gives more choice for a party if they need 1 more whm or DD.

Well, as I said I dun play pally so I'm not sure how it goes,
but generally speaking this is my thought when I was thinking about how to differentiate between pally and warrior