Having an MMO feature solo-friendly content and story progression is a great thing as long as it doesn't come at the cost of multiplayer content. Because at the end of the day, the genre is literally called "Massively Multiplayer Online." Wanting an MMO to forgo multiplayer elements in favor of single player elements is literally nonsense.
Could you imagine if we applied this logic to any other genre? "Well a lot of turn-based RPG players love First Person Shooters because they like slower, strategic combat. That's why we need to stop making Call of Duty feature real-time combat, to appeal to the people who don't like First Person Shooters in our First Person Shooter."
Yeah, that would go over so well...