Oh yeah it is clear it is a dev problem, especially after an interview with a pvp dev that left blizzard that revealed their process in many decisions including refusing to balance for months on end which is why I dont believe the problem is simply one dev, they argue and agree together on things so there's a big number of devs who hold the similar mentality of seeing casual content as something "inferior" or simply focusing and protecting their "elite" high end players above all which has the same result really.
The issue with WoW right now is that even if the dev team completely changes from the ground up, the community has degenerated far too much in all levels of play, the amount of tryhards, meta slaves and elitists are everywhere even in low end content, and mythic is even worse because you are expected to be a complete metaslave tryhard, they have completely forgotten what was meant to be play a class or spec for fun or even the challenge of trying to think and figure out how your own comb could deal with a boss' mechanics, all those have been abandoned for their pursuit of prestige and we are talking about guilds that are very very far from World first so it doesnt matter how fast they clear, they wont lose anything other than prestige which sadly their self worth and ego lies on.
The devs nurtured that attitude and unhealthy mentality by repeatedly focusing and pushing high end content at the expense of everything else, by refusing to balance classes leading to broken specs that last and are being abused for 6 months or more, by never really doing much about toxic behavior so their community knows there's no point to even report anything since nothing would happen anyway unless 30 people reported them at the same time.
And when a community is so unhealthy I dont think there's any way to fix it because the way things are now people either accept that mentality or leave which of course makes the game pretty unfriendly to new or casual players. You can always subtly influence a community as a game dev but once you created a monster it is almost impossible to control without extreme measures. (And seeing how they completely dropped the ball on faction balance and let it go out of control I doubt they ll do anything for this)
FF14 has WoW beat in most areas design wise, especially on casual content and the few positives that are left in WoW are completely overshadowed by a terrible community which you cant avoid because they are everywhere, and it gets even worse if you want to do high end content.