Might be dumb, but short of making it aoe, which would step on the toes of brutes and tanks excessively, how about other effects depending on the power set? Like, debuff recovery on elec melee, debuff defense on katana/broadsword, recharge on psi, etc. You would only use this on big bosses (dunno for sure, but I think is the main use case currently). The idea is whatever debuff your set does, it does a slightly better version of that. Then adjust the recharge and end costs to reflect the functionally, but have the base taunt duration long enough so you can perma that aspect on one target with engagement easily. You'd have to make something up for certain sets like EM, where your debuff is a control. But this would also make things less generic, which I always like when it comes to sets.