[Sabaron]

The WHM and the RDM are best used in a mutually exclusive sense. A WHM heals so efficiently and resting produces such high returns that with Sanction and SMN or PLD sub, the WHM only needs one refresher--a Bard. Red Mage can self-Refresh which is why they're useful. Most of the good setups my LS has found at high-level do not include a RDM and a WHM. They're best either/or. WHM doesn't mesh as well with COR, however, and you have to have a NIN tank. RDM can go with either tank and a COR can effectively replace the BRD in said parties. WHM + PLD is overkill most generally since a high-level PLD usually doesn't have too much trouble healing (a PLD imo is always the main healer). Additionally, a PLD always needs a targetted Refresh, so having a BRD/COR as your only Refresher creates problems since the PLD will generally be in range when they're trying to buff the front line--thus PLD + RDM > PLD + WHM.

So basically, my feeling on the WHM issue is this:

High-level WHM main Party setup:

WHM + BRD + NIN

High-level RDM main Party setup:

RDM + BRD/COR + NIN/PLD

RDM is more versatile in this respect. If you put them both in the same party with a BRD or PLD, someone's going to be at full-mp and you'll probably have a RDM Nuker which imo is generally inefficient, but I don't mind it as such what with the skill up and all (BLU and BLM are better choices for an mp-based "nuker", their spells are more efficient).