Wrong. A guilds ability to clear content is greatly increased because Second mains, Alts, boxes ect are significantly better geared. On top of that alts/second mains can wear some of your mains gear and will obviously be better played if you do main raid+alt raid on a separate days/times. AoC are also generally more time efficient then Open world.
Alt's also become much easier to level with Free loot. Ultimately the question becomes if you're gonna be part of a guild that raids 30 hours a week would you rather have 30 hours of scheduled raids or 15 hours of scheduled raids+15 hours random raids.
I can see Bat Phoning in Classic+RoK simply because of how little raid content exists, but later expansions you effectively have infinite content to do in AoCs.