If your group can kill the boss without running in to DPS trouble then you shouldn't feel compelled to DPS as a WHM when you are having MP issue.

Medica 2 is not necessary in T10, even though I mainly use it when switching out of each add phase. This is because the damage in T10 is not raid wide other than when dealing with specifics mechanics.

You do not need to use Medica to top every ones HP after Heat Lightning. If you are hit by Heat Lightning then you will not be dealing with Tether or Wild Charge. Also no one should be clipped by Heat Lightning. Also you'll have everyone spread out in T10 and when not dealing with Critical Rip or Prey you'll be able to use Cure or Regen to top people off. The SCH fairy is very effective in topping everyone off.

Avoid using Cure 3. It is very expensive and there are a handful of situations where it is effective. Instead use Medica and then use Cure and Regen to top people off.