First of all just want to point out that for holding threat as a tank you shouldn't compare other tanks to Dark.When Dark knight was being released SE knew the main player demographic for that job was gonna be people who never tanked in their life and would choose the job because it looked cool.Hence why Darks emnity is so rediculously broken.Hoping that gets nerfed in the near future.They made it a complicated class to master but designed for retards to be able to hold agro.
Like others have said Pld pre lvl 40 will be dificult to hold agro.One bit of advice i wil give especially in PLDS case.If some trash monster steals agro off you i generally stun the mob first before useing an agro combo to get it back.Reason why.The stun gives you the window to take back the mob emnity without the risk of the dps getting killed or stealing heals from you as tank.