I think the premise here is a little too thin to support the question being asked. A few problems jump out:
1. Defining a “long campaign.”
You set the bar at 2–10+ years, but years are a poor metric. Some groups meet weekly, others monthly. Some run marathon sessions, others barely squeeze in two hours. A 40-session campaign might span a single year or four years depending on scheduling. Longevity is better measured in sessions or arcs, not elapsed calendar time.
2. What even is a campaign?
This isn’t clarified. Is a “campaign” a single, continuous storyline with the same characters? Or is it multiple arcs in the same setting? Many groups rotate characters, GMs, or even systems while staying in one world. Others call a 12-session adventure a “campaign.” Without defining terms, it’s hard to make meaningful comparisons.
3. The binary framing.
You draw a hard line between “kitchen sink” (broad, flexible, potentially diluted) and “narrow genre” (focused, immersive, potentially repetitive). But that isn’t inherent. Forgotten Realms can be run with strict thematic guardrails (e.g. low-magic frontier) and Dark Sun can host wildly varied tones if the GM layers in politics, survival, horror, mysticism, and so on. The categories are more porous than the examples suggest.
4. The supposed link between setting and longevity.
This is the weakest part. Campaign duration isn’t dictated by whether the setting is broad or narrow. What actually sustains long-running play is the group itself:
- Are players invested enough in their characters and story to keep coming back?
- Do they want consistency, or do they crave novelty and rotation?
- Does the GM adapt to shifting interests, or rigidly hold to a plan?
- Most importantly, do people actually have the time and social bandwidth to keep showing up?
The truth is you can run Ravenloft for a decade if the group wants to “live in” that story, or burn out on Golarion in six months if the energy fades. The determining factor isn’t the scope of the setting — it’s the culture of the table.
5. The deeper issue.
If anything, the real question here is about player psychology. Most players don’t want to stay locked into the same character and storyline for 5–10 years. They want to try different classes, roles, and experiences. For the rare groups that do sustain that kind of continuity, what’s happening is less a “campaign” in the game sense and more a lifestyle hobby: the table has created a shared fiction they want to inhabit indefinitely. At that point, the particulars of the setting are incidental. The world could be Forgotten Realms, Dark Sun, or a homebrew; the longevity comes from the fact that the group has chosen to treat that game as a long-term shared culture.
So if the question is, “Which type of setting better supports a long campaign?” my answer is: neither, on its own. What matters is whether the group wants to keep returning to the same world, characters, and shared narrative. The rest is just backdrop.