Don't forget that Attunement also raises AGL to a lesser extent. So they were aiming for: Melee focused build? Level up ADP: Increases i-frames, item consumption speed, poise, poison bonus and different resistances that are key for close combat; Caster build? Level up ATN: Increases i-frames and item consumption speed but not as much as ADP, spell slots, spell casts and casting speed.
Sounds good on paper in terms of build differentiation (casters can attack from a distance so this compensates the less amount of i-frames and item consumption speed). To me, it makes sense that a melee trained warrior is better at dodging than a mage but in the end, it fell short on execution. It also doesn't help that you gain a lot of levels in DS2, so it is easy to overlevel.