To the OP, there can be only 2 options for Shield Bach:
1) keep Shield bash as-is and keep it's identity and utility
2) change it to an OGC skills, put a 20 sec CD and reduce the potency to 50 and it become WAR's Brutal Swing. If it was any different than that, it would be completely unfair to WAR

PLD is the only class that can stun for a extensive period of time (all other class have it OGC but with a 20s minimum CD). I don't know why we'd want to remove that ability that PLD only has.
Also, every fight is a team effort and if the PLD can't afford to interrupt its enmity rotation without loosing aggro, the issue is definitely somewhere else... Only a PLD OT can come close to stealing aggro, no other class should pose a threat.
Heck, War is able to maintain aggro lead by only using 1 enmity combo for every 3 combos (to maintain SP and SE debuffs).