Major failure, our guild was casual but still cleared mythic before next tiers release in MoP and Cata, but with failed mergers and lack of good recruits, we couldn't make a steady mythic team all the way through highmaul and brf, we finally ended up throwing in the towel after beating archimonde HC 2 weeks after hfc release, but still short on players for mythic progress.
This day none of us raid, and only 4 of us are even considering raiding in legion. I laugh at the people who say "only weak guilds broke in this expansion", you're the kind of person who contributes so little to your raid that you dont see the massive amount of work that is put in by officers when not raiding. I'm sure you haven't had to "take shifts" recruiting everyday of the week in trade. Or had to seek out and negotiate mergers with other frustrated 10 man guilds. Then having to deal with pissed off players that progress is happening too slow, because the 50% increase in roster came with social challenges aswell as cultural challenges.
This is a game, it shouldn't take so much management just to get into the challenging content. It's enough of a barrier that you have to commit to raiding x hours a week.