No, Cata crashed and burned because of Heroic dungeon tuning. We know this is the case, Blizz knows this is the case, have stated it is the case, and have never in any subsequent expansion released anything like Cata tuned heroics. Heroics were THE casual content in WoW at the time, and tuning them the way they were at launch was a significant error. Ghostcrawler writing his blog about how hard they were was a worse error. They effectively cut the majority of the player base off from the one activity enjoyed by the majority of the player base, and then told those players in no uncertain terms "tough shit." Hell, you could struggle to get through Grim Batol on normal during the first week or so if you didn't have a guild group. Good fucking luck running heroic deadmines in a pug pre nerf. Why am I going on about this? Because WoW does well when casuals have content that feels rewarding, and the second that went from being true to being not true, WoW's numbers went off a cliff. It wouldn't have mattered what order the expansions came out in, WoTLK would have been loved for giving people puggable heroics and raids.