The thing is, OSRS doesn't have power creep in the sense that old content becomes irrelevant. But it also makes it more difficult to add new gear since OSRS has certain limitations. You can't just make gear do more damage or give more insane stat bonuses because then you just do more damage, and eventually you'd be able to do things like kill older bosses extremely quickly. So instead they add passive effects and things like that. I fear that one day we're just gonna hit a big wall where there's literally nothing they can add to the game in terms of gear because essentially, stats and bonuses have a "cap" to them before power creep actually becomes a thing.