I think you overstate the complexity of tanking by a fair amount.
Both PLDs and WARs should not have a problem maintaining aggro. Flash/Overpower 3x and you're guarenteed to have aggro unless the DPS vastly outgear you.
The difficulty in WAR comes in appropriately keeping Maim/Storm's up, not overspending your TP, and using your Infuriate on the right moves in preparation for incoming damage.
PLD is very much passive in its mitigation, and only has 1 combo, and no buffs to maintain. Reactively using Shield Swipe does not really account for much skill, unless it's used on a mob at the right time to stop a weaponskill or something. Using Cover is pretty much a "Use on the WHM or BLM" thing, too.
PLD and WAR both have differing skillsets, but WAR is more complicated to play than PLD in measurable ways.