I believe more information is needed for you in order to understand my position on the threat issue I have. I'll present you with two situations for a more concrete representation.
1. Situation one involves an encounter of 5+ enemies with some on my left and right flanks with one or two in front. Given the task of maintaining aggro on all of them in 9/10 dungeon runs is fairly easy. There are rare instances where either two DPS will focus on differing enemies or they begin to focus one down as I'm doing an aggro rotation through all enemies. To get back to my original target will take a minimum of 6-7 GCD's, which even with flashing and a Circle of Scorn leading up to my initial target, will present me with seeing a DPS up to 80% or greater of my aggro bar. Assuming the initial target received not only Shield Lob but Circle of Scorn, Flash, Fast Blade, Savage Blade, Flash, Rage of Halone and another Flash just for good measure, as I'm coming back to it I'll know that a DPS will be fast on my heels.
2. Situation two involves only a boss encounter. I'll initiate the encounter with a Shield Lob in Shield Oath and maintain it for a minimum of three aggro rotations with a couple of Flashes and the Circle of Scorn included. Transitioning to Sword Oath to begin DPS rotations I knowingly have to pay attention to my aggro bar with each successive Royal Authority and Goring Blade as is to be expected of me. Occasionally after every third or fourth Royal Authority I will add in one Rage of Halone combo to limit how fast the DPS catch me in terms of aggro generation. While I will never explicitly lose aggro, seeing others approaching the top worries me greatly. In one such encounter we finished the boss and I only had slightly larger than a sliver off aggro generation left.
In both situations one would be wise to ask "did the DPS use their aggro limitation/reduction abilities" first in order to give the benefit of the doubt to the player in question. From the observations I can make in the limited time I have, I'd have to say sometimes yes and sometimes no. I'll agree with the statement that as long as I'm in Shield Oath there won't be a considerable issue.