Source is official blizzard reported numbers, which was reported on this website back when they were still doing it.
My friends list was an annecdotal example (that many other people shared during that expansion), of OG Warcraft players who had also played the RTSes, and who felt like Blizzard had lost touch by that time with the core Warcraft theme, and were diverging on pointless threads, themes and memes.
It is no secret that the expansion's new zone had the weakest lore ever written, its only redeeming features being the purge of Dalaran, SOO with Garrosh's arc and the Klaxxi.