My impression is that Marcus wasn't thinking about other people reading this stuff at all, but just making little reminder notes to himself, in which case of course there are going to be reminders that repeat over and over - we all have our pet topics that we circle back to and our characteristic struggles that we grapple with over and over again.

Marcus's thoughts on death seem to be pretty characteristically Stoic, so I think the ideas must be less modern than they seem to us. The Christian idea of death superseded them, and then as the Christian view receded the "atoms or extinction" view came back to the fore, and seemed new because it was so different than the Christian view.... but really it was just the tide turning back toward an older view.