Generally I'd look for what spells should be in the top usage more than comparitive "numbers."
A correctly-played disc priest should have:
1: Spirit Shell (@30%)
2-4: Divine Aegis, Prayer of Healing, Atonement (@15%)
5+: Prayer of Mending, Power Word: Shield, Penance, assorted misc. effects (<15%)
(note: this is changing in 5.2. PWS goes up, Spirit Shell and Divine Aegis go down, amounts to be determined.)
A correctly-played holy priest should have the following effects listed and making up the overwhelming majority of their healing, with usually no one effect accounting for more than ~20% of total healing (the order will vary):
Divine Hymn, Prayer of Healing, Echo of Light, Prayer of Mending, Circle of Healing, Renew, Lightspring/Lightwell Renew, Cascade or Divine Star
A correctly-played paladin should have:
1: Illuminated Healing (@25%)
2-4: Eternal Flame or Light of Dawn, Holy Shock, Beacon of Light (@15%)
5+: Divine Light, Holy Radiance, Light's Hammer, Holy Light, Daybreak, assorted misc. effects (<10%; HR may go up to the 15% category in 25m, DL may do the same in 10m or when tank healing)
I don't know the current iterations of shamans/druids/monks very well. I do know that shamans should usually see Healing Rain on top, monks Renewing Mist, and druids Rejuvenation, but beyond that I'll leave it to the experts.