There are already two dps-tank jobs, please don't make Paladin the third.

[Duelle]

Thing is, as we can see with Heavenly Heel, it's wonderful against PHYSICAL tank busters with a cast.
It'd eat Flatten for breakfast. It's more victim of circumstance than a bad ability.

At least in my own experiences, auto attacks still process while a boss is midcast and preparing high damage attacks, so the element that devalues Sheltron is there. If the intent of the ability is to guarantee a block because of a big incoming hit, turning it into guaranteed blocking for 5s basically meets that intent while giving some leeway.

For its animation and the niche it seems intended to fill, an extended block would make a lot more sense, and would certainly give it more significance in AoE pulls, but I don't think it's exactly necessary either. First block + 1.5 seconds thereafter would be more than enough time. I'd be more inclined to say that it and/or Bulwark's inability to affect magic damage taken whatsoever are larger points of evidence of a broken toolkit.

5 seconds isn't that much time, to be honest. Uptime would still be pretty low considering it'd still have a 30s cooldown.

The devs have already said something to the effect of never allowing shields to block/mitigate magic, so that particular point is not worth pursuing at the moment.