Yeah, rdruid is definitely a secondary healer at the moment. Same with MW. Currently the ranking purely on healing power seems to be:
Tier 1: Either priest spec
Tier 2: Hpal & rsham (hough if you maximize their utility I'd say its overall value can be tier 1)
Tier 3: Mistweaver (though it has slightly better heals, similar to rdruid it's better as a secondary healer)
Tier 4: rdruid (though if doubling as backup FC, its overall value goes up)
Note: we've only shown real data for disc, hpal, rdruid in this thread. The above list is based partially on that data and partially on anecdotal experience. May add the other specs here later if we get time to play a few more representative games on each.
Note 2: this is for f2p, the ranking could change at 29 with the addition of new spells.