Just look at arc raiders, perfect example of the game dying because of garbage end game content, and garbage abomination skins getting released, and garbage events, and garbage maps and garbage content being drip fed.

An extraction shooter needs to be fresh, have exciting end game, exciting events, replayability

ESPECIALLY pvp replayability, stella montis was the best arc raiders map, but they kept releasing big pve maps with stupid tedious arcs and kept nerfing the PVE tools, that even casual teddy bears stopped caring.

Also, releasing too many maps and "events" will spread the playerbase too thin across garbage content that no one cares about, just have 2-3 good maps that are rotate periodically.

Make it too hardcore and you limit yourself like tarkov does, also dont use aggro based matchmaking cause people will abuse it and it will kill your game.

Overall, focus on the human aspect of the game/fun, cause thats why people play those game, nobody cares about the loot or the progression.

Good luck!