Utter bs.
Yes, you can have a million heroes running around. It's your personal context. It's called instances and phasing. They've been around for a while now. You can single handedly save the world/galaxy/whatever. Then they go into their instance and they do it, too. This isn't new. Even WoW had countless instances and quests that aren't raids. All important events were not exclusively in raids.
You can handle a narrative outside of raids in an MMO. In fact, it's been done. The conflict you think exists is an imagined one.
Maybe this revolves around your idea that MMOs are about being a part of a large universe of other players. Increasingly, many of them treat the universe as just the meeting ground. The other players influence on your narrative is unnecessary.