I think 20 seconds on the recast is a bit extreme, 10 seconds would be a little more in line imo.
It would help, I guess, if I understood the rationale behind the change to 20 seconds versus 10 or 15. It seems to me that a 10 second recast meets the the criteria of "these were meant to be an addition to the aggro management, not the aggro management itself", in taking the ability to use them as THE aggro management, while leaving them as a useful tool in the rotation.
If theres an objective reason specifically why 20 seconds is necessary, I would be happy to have it pointed out to me.
My personal feeling, where things like this are concerned, is the lowest possible reuse that would meet the criteria of forcing the player to use other things, while leaving the pants useful. I just don't see how 20 seconds is the minimum necessary to achieve that.