I disagree in part. Some people can't rank on many bosses because of the strategy. E.g. Immerseus, where some people just stay on the boss (no AoE) and heal in most split-phases to help out healers. Or Shaman / Nazgrim / Malkorok, doing offtank- and soak-stuff. Or amount of cleave possible (e.g. protectors, tanking together or not, or spoils - mantid or mogu side). Add to the different strategies, that the combatlog on some bosses (e.g. Norushen, Spoils) has some problems with range / different phases. So just looking at overall rankings can be skewed.
And, because you were not sure: A guild on our server killed Garrosh 25m hc last week iirc (Advance - Azshara EU), raiding 19 hours/week - though they have stocked up the first week in this tier, raiding about 30 for that week.
Though I think the discussion goes a bit offtopic here - hope that's not a problem, since the question in the OP was already answered.