I haven't played the game so I'm just postulating, but I think its the only message that makes sense, give the context.
It doesn't need to make sense story wise, its a game... but yeah it does look similar to no man's sky, but the game is literally about delivering packages and overcoming obstacles, no man's sky isn't such a game, those items in no man's sky is unlikely to have a greater impact to gameplay than the items you find in death's stranding.
I haven't played Death Stranding either, only saw reviews and let's play, so postulating also.
My reference to No Man's Sky was about the fact that in that game, you are supposedly occupying the same world as other players, you may see traces of them (like planets or creatures they found first and named) but you will never meet anyone (talking about the initial release, face-to-face meeting eventually got added a couple of years later as free update).
As you said, this game is literally about delivering packages (balancing yourself, walking simulation, inventory management), that's the 'one idea', the core mechanic. The rest (the baby, the pseudo coop, the stealth, the combat, the social media, the story, any social commentary about America) are just things added to stretch it out to a game. Some of these added ingredients add to the world building and perhaps gives some emotional connection to the player, but it's still about delivering packages (aka fetch quests). To me, some of those (social commentary messages etc) seem very superficial, artificial and manufactured, unlike say Bioshock series. Anyway, I don't read too much into the story of a Kojima game
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Edit: Oops, got confused, I didn't watch let's play on this one. I think still under embargo? Was watching Outerworld let's play. That one the writing is really sharp, the dialog is so funny.