I've been running with the glyph this past week for raiding, so next week I'll run without it and I can compare my healing done with it, to see if there's any difference.
Just by looking at it, I personally think it's a healing loss, just like Allorah said the 2 second longer cooldown for just one person really doesn't add up in my head as logical. I just haven't actually taken the time to take off the glyph, but I'll make that a priority for this next week of raiding. Then I can compare and contrast the logs.