If we were living in a simulation, why would our perception of relative time be absolute relative to the simulation? Why wouldn’t the simulation just simulate slower at whatever level of abstraction it operates on, causing us to be none the wiser, like the AI in a frame-locked videogame?

Human perception isn't a consideration of the simulation, we are just a side-effect.

You can either simulate the entire universe in infinite detail taking infinite time, or you can optimize to focus on the more important bits in finite time.

It might be a limit to precision too if infinite accuracy requires infinite space.

For low energy an approximation might suffice, and that would go some ways to explain quantum effects.

But then it doesn’t matter, because what’s at the top of the simulation tree?