Momentum isn't too hard to do. Build up a stacking speed and damage buff, and then have a hitstop move that consumes some of your stacks.

But if you want to build unique tanks, you really need narrower concepts for each. It would also be cool if WAR had a jetpack and could teleport and and could shapeshift and could turn undead. But maybe it's fine for them to be the BLM equivalent of tanks and do the slowest but the biggest hits so that we can develop some other unique tank concepts in the future.