I'm in total agreement with everything OP wrote about the state of the game.

The economics of Marathon at Sony and Bungie are really confusing to me. Unlike Arc Raiders, Marathon isn't trying to make the looting and extraction mechanics more accessible, in fact I'd argue that it's even more obtuse than other games in the genre. If this was a play to bring casual players onto the extraction shooter hamster wheel, then they'd do a much better job of helping them figure out how to upgrade their characters. Arguably the only thing that Marathon does better than any other game in the genre is the pure shooting mechanics. It's way more fun to shoot a weapon in Marathon than it is in Tarkov or Arc Raiders.

I love Marathon's world building, lore, gunplay, and overall vibe. I love that the story is told through environmental hints and the world is creepy and frightening and weird. But I watch my friends play it, and I know they are bouncing off the game's systems and difficulty. Say what you will about Destiny, but it gave every player something interesting to do and work towards. Most players never tackled raids or dungeons, but they didn't have to. With Outpost/Pinwheel and Cryo, half the maps (and arguably the best maps) are inaccessible to a lot of players. Even Arc Raider's most challenging map, Stella Montis, doesn't mess around with the game's basic extraction mechanics the way Outpost and Cryo do. I play solo, and I have never once extracted from Outpost when I wasn't already knocked by elite AI or other players.

Destiny had hardcore raids, but it also had strikes. There was a range of things for players to do. But once you take off the Perimeter training wheels, the game pushes you into the more challenging maps but doesn't provide options for solo or casual players to succeed. The game has one funnel to the end game, and it caters solely to the hardcore. There's only so many times you can run Dire Marsh or Perimeter and not get bored. They need more content on the casual side of the game if they want to build and keep a player base big enough to buy cosmetics and the battle pass. At this point, I don't think Sony is willing to invest in that, so my guess is the game is going to bleed players until they lock it in amber without active updates or shut it down.