I'm not convinced this is that much a limit. Perfect dodge would fit an evasion tank very well. As it is we have turtle and blood, evasion is the only classic tank paradigm left. That said our current blood tank isn't that... bloody. Both classes have the same effective hp, and actually if you break it down over time, warrior can mitigate more damage from cool downs than paladin can (excluding hallowed ground) via cool downs (note this is not counting shield oath).