I'll give you that r14 grind is mega tough but at that point you can compare that to very top guilds that grinded islands 18hours a day for a week and grinded out 5 characters before tier begins.
No bosses die in few seconds still compared to classic, fastest kills are 90 seconds basically. They all require at least 1 healer and thats on early bosses only. Later bosses still require you to do mechanics and more healers and take a while, even early bosses require you to do mechanics cause you only have 1 healer. This is also deep farm with insane corruptions, prog is long over. Everyone knows gear growth is insane in retail between tiers and end of x-pac always gets ridiculous with power gains, using that as example is stupid when completely ignoring difficulty of mythic during fresh tier release.