Shameless plug, but here's a video of us running a 5 chest DH run with 4 players.
http://www.youtube.com/watch?v=0H-vgjk0saE
We heavily abuse WHM in the run, but it has nothing to do with the job's healing capabilities. Due to the near-broken strength of Regen, you can basically play WHM as a full time nuker that Regen's every 45 seconds in non-boss situations. It's easily the most broken job in 1.21. I personally go with 5 WHM builds right now...
Max Healing Potency only - bosses with consistent wipe moves (e.g. Coincounter 100tonz)
Max HP and Healing Potency mix - most bosses
Max Enhancing / DEF / VIT - large numbers of trash mobs (instances, strongholds) - also my default gear
Max MATK / Enhancing combo - trash mobs with heavy emphasis on damage dealing
Max MATK only - Limited use, but can be devastating if using a planned Holy strategy (start 18:10 in the video to see an example of this)
For those that play XI, WHM is much more similar to SCH than the XI WHM. Your nuking capabilities are much better in XIV. Gear swapping is a royal pain in the current XIV, but if you macro, it should only take max 10 seconds to get your gear swapped. WHM is the most versatile job right now - best healer, very capable to sometimes best magic DD, and above average at survivability if built right. You want to be able to use multiple gear sets to augment the job's innate versatility.