I have been level designing since Unreal 1 days, so that chips in for me, roughly speaking, 15 years of experience in level design.
Back in the day, the joy would be to hunt for games based on unreal engine, of which released mod tools for us to salivate over. By then, downloadable content would mean “free maps & missions”, capitalism had not set its gloom over business of game development in those years. Everyone was freely exchanging mods made by the modding tools by the ever-inspiring modding communities and the term “shelf life” meant something special for both publishers as well as developers during that era.