A 16% bonus from 15% of a heal, realisticallt speaking it might not be there.
Triage, how many healers you are working with (or against, depending on your guild group) actual encounter mechanics...And why wouldn't spreadsheet math not apply to healers? Killing a boss with damage abilities is no different then bringing someone to full health with healing abilities. That point is moot.
Tell me, what encounter allows all healers to take advantage of 100% of their crit rating, cooldowns, full HoTs rolling, etc? Dreamwalker.
How many Dreamwalker fights are there? None so far. Spreadsheet math works because including RNG and unlimited time, the boss' health goes down in a linear fashion.
People's health pools don't start at one and have an entire fight to boost themselves up to full. Damage comes in bursts and needs to be countered, and no spreadsheet will ever compare against real encounter experience.