The only time I have an issue with threat is on Titan HM if I am solo healing it and the tank is less than spectacular. Otherwise, a single medicaII during tumult (allow it to tick and top people off paired with the other healers group heal, do not over heal) or cure III during jumps should not cause threat issues besides the first jump. Keep your Shroud up and blow it after the first jump when Titan lands to allow the tank to get back ahead then on cooldown for mana management and periodic threat dumps. If the tank is still losing agro then the Tank is poor at enmity generation and it is not your fault. As long as you are not throwing up regen before a pull there is no reason not to use it. I personally wont put it on until after the first jump as the damage on the tank is minimal and most of the regen is wasted just adding unnecessary threat, but after that you can keep it rolling.


I am not sure if you are WHMing wrong as we cannot see how often you are casting aoe heals, but it is likely the tank was either new and undergeared or bad, if you were not spamming aoe heals. I personally can dps and heal without issue on extremes as a whitemage without having a threat issue.