The problems I see with the "competitive pve scene".
1. The game is buggy as hell. There were always bugs, but I don't remember that many and that gamebreaking since vanilla / early tbc. Bugs in raids, quests, class mechanics, everything, some of them just irritating, some exploitable. And fanboys keep defending Blizzard "oh but programming is hard work"... Being a chef is hard work but you wouldn't defend one who burnt your food (oh hai Nomi), and generally that applies to anything you pay for, if you pay someone to put wallpaper in your room and it's sloppy and ungluing itself or has wrinkles, you'd complain too.
They manage to break every simple small thing, they even broke font in 7.1 on non scaled default UI so I had to use an addon for 1,5 weeks before they fixed simple thing like that. My demon hunter could not loot the flower mobs spawning in garrison garden, since the creation until I actually levelled my herbalism and left garrison, I heard that is fixed now, but not sure, took them months, and that was applying to many other mobs like MOP worldbosses. The smearing portraits bug exists since the implementation of new character models and it's not fixed for a second expansion in a row. They also managed to break my druid's transmog helmet by changing its size to too big while it was fine during WOD.
And people had way bigger bugs like if you had hunter pet with prowl, it would bug your main action bar, druids had multitude of bugs with their order hall campaign (not receiving 3rd relic slot, getting all of their bloods removed instead of just 10 etc.), many other classes had bugged quests for secondary artifacts or second grade of troops (especially hunters and paladins).
Maybe they should stop with their philosophy of change for the sake of change (things like revamping classes / specs every expansion or tampering with things that didn't need to be tampered with like nameplates or character panel), and concentrate more on polishing and bugfixing so less gamebreaking and exploitable stuff goes live. Within a week we had 1 banwave for world quest AP exploit and second one for Helya... We had 2 out of 3 bosses in TOV being bugged...
Many MMOs flopped because of too many bugs in game at launch (Wildstar, ESO, SWTOR), WOW is a powerhouse but doesn't mean Blizzard should get sloppy with their QA.
2. Blizzard fails to limit no-lifing giving advantage in this game, even worse, this expansion they encourage and embrace it with the legendary system... Play endlessly and keep hoping you hit the jackpot!
The world race scene dwindles since Cata when split raiding and maintaining raiding alts became so widespread you couldn't compete without it and with it the game becomes a huge timesink just for a "smile and handshake" if you succeed.
The current system encourages levelling bazillion alts, grinding few hundreds m+ on each of them and then cherry picking the ones with best legendaries because they increase your performance by 10-20% and that's non negligible in a cutting edge progression. Before such power would be locked behind set bonuses or trinkets but with split raiding and master looting you could target who receives what. With legendaries, no way to target them, no way to distribute them and decide who should get what, it's just a lottery, keep throwing your resources at it.
The class balance rollercoaster also requires people to keep alts and offspecs and constantly switch, and with artifact power (apprently atm if you don't have 35 points in your spec you are not progression viable because you're missing 5% of your dps) and legendaries that's a massive grind on multiple characters / specs.
I thought artifact knowledge was supposed to reign it in making no-lifers only 1-2 traits ahead of casuals, atm the gap is 5+ ranks...
It's a lot of effort for little pay off and I'm not surprised guilds like blood legion decide "fuck it, we're quitting / going casual".
Players who want to get something out of their gaming hobby switched to hearthstone and overwatch. At least there you have tournaments with prizes and guess what, there's less punishment for a situation "my character got nerfed" because switching to something else is way easier.