Destiny is the Diet Pepsi of video games.
Your metaphor isn't helping.
I call "watered down" when a game spoonfeeds itself to a wide audience. On Hard, the gameplay is an actual challenge, and not something people can just mouthbreathe their way through. On a story level... it's almost the opposite of "wide audience". No one except the most hardcore Bungie fans who played all the ARGs and shit even know much less give a shit who The Traveler and The Speaker and The Darkness are. It's over-esoteric to the point of absurdity. I still like the tone of it though.
On the most surface of surface levels... like the lingo, it's accessible. "Raid" "Loot" "Wizard". Other than that, your argument contradicts itself. It's a barebones coop shooter that uses the thinnest pretense of missions to facilitate people making their own stories with their friends via the game mechanics.