I think bosses are way too complex nowadays. Having 5 phases with 10 abilities each.. where people need addons like DBM or otherwise they would not know what to expect.. where raiding guilds hire lua scripters to make them raid timers..
Really.. whoever designs raids nowadays, he has a real problem what a game should be about. At least for most of the players.
I remember the good old days, when bosses were tank and spank often, with one ability you had to care about. Those were the days when i played raids as well.
Dungeons went the same way. The bosses are overly complex, even on normal and in raids on LFR. Because developers with a hardcore mindset believe their players "have become so much better".. Considering the fact that raids have been less and less appealing to normal people, they probably should think about returning to easy bossfights for normal players, and leave their multiphase bosses to mythic raiders. While i do not really believe mythic raiders would deserve such high degree of attention. They are a small minority, after all.
To me it seems the devs sit in a filter bubble, where everyone is highly skilled and completed Dark Souls without using a cheat mod. While the fact is that cheat mods are the most successfull mods for hard games.