I think the premise is wrong more than the proposed fix. Foot Knight isn’t a failed tank, he’s a stagger-support bruiser tank, and a good one. Battering Ram knocking down a whole chaos patrol over and over is something almost nobody else can do, and it’s not just crowd control. With the level 15 talents, staggered enemies take more damage, so he’s keeping the team alive and helping them deal more damage at the same time. He’s an active tank that boosts the whole party, not a passive wall. All the Foot Knight players would come after you with pitchforks and torches if you wanted to rebuild him or change his ult to mirror Ironbreaker’s.
So I don’t think tanking is his problem at all. The one thing Foot Knight is missing compared to Ironbreaker is the same thing the first three Kruber careers are all missing: ranged options. That’s a Kruber roster problem, not a tank problem, and a taunt wouldn’t fix it.
Look at the gap. Bardin’s melee kit is the closest thing to Kruber’s, but for ranged he’s got throwing axes, grudgeraker, crossbow, handgun, trollhammer, masterwork pistol, drakefire pistols, and flamethrower. Even his most restricted options, drakefire and throwing axes, are on at least two of his four careers. Kruber’s got repeater, handgun, and blunderbuss, with the bow locked to Huntsman. That leaves Merc and Foot Knight with only three ranged weapons to pick from. Kruber having fewer ranged options than the other ranged characters is one of the few things you’ll find broad agreement on, which is exactly why I’d point the fix there instead of at his ult.
That’s also why the Ironbreaker comparison runs the opposite way from what you’d think. Ironbreaker can trade his sniping for Drakefire or Trollhammer and put out serious damage clearing crowds, but Foot Knight isn’t actually behind on damage. He can be spec’d to hit quite hard in melee, harder than Ironbreaker, with access to weapons like the Bretonnian Longsword, Halberd, Executioner and Greatsword, and power bonuses that let him put out damage on par with an IB running Trollhammer or Drakefire. The gap is weapon access and the variety that comes with it. Give Kruber’s tankier careers more ranged tools and Foot Knight would have a more varied playstyle like Ironbreaker does. That’s the main thing I think he’s missing compared to IB, since Ironbreaker’s ranged option changes how you play him quite a bit.
Warrior Priest is more apples to oranges and mentally I’d keep him separate. He’s got some healing, a window of temporary invulnerability, and good melee damage, but no ranged options whatsoever. Foot Knight brings more stagger and gives the team DR and block cost (or power) bonuses, plus an ult that’s great for rescues where you have to blast through a crowd to reach a downed teammate, which almost nobody else can do. They’re both tanks, but they solve completely different problems for the party. That variety is the point, and it’s an argument for giving Kruber more ranged options, not for turning the charge careers into one more taunt.