Hpalas won't be as high as disc on most fights (unless it's one that heavily favors SS they should be up there though), but they can easily output as much healing as the other healers (and considering that part of it is absorbs that generally results in them being higher on the meters as well). They have the best tankhealing and brings the most utility of any healer, neither of these things show up in the meter. Unlike disc they don't have any big weaknesses (poor healing on the move, no bursthealing) but they hardly excel at healing massive raiddamage (which is why you'd grp them with a disc now, or a druid/mw post 5.2). Unless you already have a paladin in the raid (and possibly even then) I'd argue that a hpala brings even more to a raidgrp than a disc priest right now.