As for the Mythic KJ is hard, and took awhile No clue. I suspect a lot of had to do the mechanics at that tier of raid, probably a lot of timing issues and peeps not doing there jobs right (or the right combination).
I used to be Mainline raider and the wipes and drama was fun..... For instance I wasn't leveled for MC, but an entire zone was arguing with a know drama king who Ninjaed a valuable knife from Next to last Boss Major Domo (?)[I was paladin so I was a Buff Bot and Healer, when I did start raiding -- ZG -- Vanilla ]
Even In LFR it can be a pain (I do that as its fun and faster), like 6 wipes on Gul'Dan (even with the Echo Style boost) as people Simply where not doing the basic mechanic key eyes, stay out of green stuff....
I just complete Wing 3 of LFR ToS we wiped once on Maiden, once someone explained fight, we destroyed her, Avatar was easy....
(I can do most tiers, I am slowly losing interest there).