There is a fine line between an intelligent tank that holds back the group, and a bad tank that holds back the group.

If you find a decently geared tank that is correctly dishing out threat, and (while using quelling strikes) you still consistently pull off them, then it could use a buff. Excluding the region where item level syncing does not come into play (a fresh 50 tank vs i100 dps) I don't believe this is actually an issue. And the exclusion should actually be addressed with syncing level 50 dungeons to alleviate that difference rather then buffing an ability that effects all content.

Quelling shot is fine, the issue exists but it needs a less reckless solution to the problem. It's not interesting game play when dps have an ability that will literally make threat management a joke.