Yep, that is 100% correct. However, because dps are very overpowered in this game with respect to tanks, you almost always will have to guard the dps for the first 20 or so secs of a fight w/ similar gear/skill of course. Because tanking stats add absolutely nothing to aggro generation, the higher tier gear the group has, the harder it gets to keep aggro. You do get some extra mainstat, but the secondary stats are all tanking stats, while the dps gets secondary stats that add to dps which adds to aggro.
This is just wrong. My shadow is geared to maintain aggro against DG sentinels who go balls out from the get go of a fight, while still maintain the 30/65/60 mitigation stats that is expected of me. I haven't guarded a dps in quite some time, 50-50 laziness/lack of need. While not all tank classes are created equal where aggro generation is involved, but a blanket claim that tank aggro cannot keep up with DPS aggro is fallacy.