As an experienced WHM I have to say I found this guide to be somewhat rubbish. Cleric Stance and Holy have 0/5 utility and should never be used in a party??? That's ridiculous.

I usually cast Regen on the tank and then use Cleric Stance + Presence of Mind + Holy on big groups of adds and it does the job every time. A good WHM should heal when they must and switch to DPS to help the party when appropriate.

So my advice is, when you are still on lower levels, focus on healing. A WHM's best spell for me is Regen and should be used a lot once you get it (just wait until your tank has aggro before you cast it). But when you reach higher levels and feel more comfortable in your role, I think it's important that you use your attacking skills too. A high level WHM with good weapon/gear and Cleric Stance on is no slouch when it comes to attacking.