I can't really say anything new that you don't know already - obviously healing meters aren't that good for measuring a healer's capabilities. Probably the only way to actually see if a healer's doing his job is to actually watch a PoV video of it; or put on a bit of extra stress (i.e. 2-healing instead of 3 healing a 10 man raid) and see how they manage.
From that last point, another factor to consider is to see how many healers you're running with. If you're running with too many some healers will get bored and won't have much to do, and as a result be lower on the meters than others. (This may be the reason for your Holy Priest's mentality)
Some classes will obviously top the charts more than others. Resto Druids due to their HoTs mostly being fire-and-forget (although I've never played one so this may be a gross generalisation!). Disc Priests will be lower on the charts since most of their healing is through absorption (shields) unless you have the appropriate logs/recording means to calculate them in.
I don't mind healing charts being posted because my guild is fairly casual about it, and I like to joke about it with my fellow healers since I'm the only Disc Priest in my guild but can hold my own in skill. Plus I'd done all my research before I took on full-time Disc Priesting, I knew I'd be near the bottom of the meters; my heals won't heal for as much; my arsenal is more limited, etc.