Agro "pong" can be a lot of fun, but it's one of those games the "ball" doesn't appreciate as much as the players. I still recall the good ol' days in EQ1
lane of Fear where two wizards could stand on opposite sides of the field and make the entire raid run back and forth .. back and forth .. back and .. "ok, jokes over, cut it out or get punted!"
DDO agro isn't as simple as "total DPS wins". Sequence, frequency, magnitude, and distance all seem to be factors.
Most "tank" builds that hit forums filter down from the push-raiding crowd where the tank needs to sacrifice all dps for ttl. It's quite possible to run a DPS tank if you're not push raiding and do very decent DPS -- mine does maybe grade-C DPS (about like a swash), which when multiplied just glues stuff. However, while my tanks are great for R1 raid and R10 quests, they'd fail hard on push raiding.
My two real DPS will pull agro (melee threat-30, ranged threat-70) on occasion, but by far the worst agro offender I have is this junky 1st life INQ HC rebuild with threat-70 that doesn't even do as much DPS as my tank. Imbues are buggy as hell for threat.