I think what's obvious to everyone here hopefully, is that no one was "offended" in terms of being shocked.
They were "offended" because it was awkward, disgusting, and a terrible performance.
It was embarrassing for her.
Like you said, from a purely "moral outrage" standpoint, Marilyn Manson was twice as shocking 15+ years ago. Lady Gaga's bare ass probably drew more ire from the moral crusaders.
Miley playing vagina peek-aboo with that stupid fucking tongue-sticking-out face bothered me on the same level as seeing a homeless woman pissing standing up on the street while eating garbage.