it is as simple as Dungeons and Dragons, they nailed it with Warrior even that it is not as balanced as others IMO.

Most games merges Dark knight and Paladin to one class but 2 different specifications, but since that in FFXIV we have them as different jobs I think DRK should be in the middle of PLD and WAR, a job that have both but less specialized.

PLD block and use defensives + active block, WAR restore percentage of the damage received and regen with high health pool.

DRK can have active block and life steal.