I agree, and say we are in a simulation. I'm not sure what the precise definition of 'simulation' is, but it should be a broad enough concept to include the universe, whatever the universe is. The universe may not be a directed simulation, it may not be a simulation that has a beginning and an end, and even the continuity of it may be a complete illusion. But I cannot imagine how anything at a sufficient level of detail could be interpreted as not a simulation; that is, as something that isn't computed or doesn't run with some mix of mechanical and random rules.

In the context of the point of view that everything is a 'simulation', if "actual reality" is fragmented or in any other way fundamentally really, really different from my subjective experience, I don't care. I care about understanding the reality of the simulation I'm in. I only care about any reality outside the simulation to the extent it affects my simulation. And I believe I'm thoroughly justified in this focus of interest. If everything is a simulation, why should simulation B nested within larger simulation A be less "real" than A? I have no evidence that simulation B is fragile or inconsistent, so that I need to be prepared for A tomorrow.

If Nemo told me today that this world is The Matrix, I would be very excited at first, but I would also temper my excitement until he answered my question whether any of the rules are different inside the simulation than what we thought. If there's no magic, no way to get the simulation to do something cool, then ultimately it just wouldn't make a difference. Reality is as real as it ever was.

A 'less real' reality is only a reality that is inconsistent, that provides evidence of a parent reality that is arbitrarily manipulating the simulation in some way. Thus finally, I would define a simulation as "subjectively unreal" only if the simulation is impossible for the subjects to model without a model of the parent.

don't think there's a meaningful difference between "the real world" and a perfect simulation of it (at least seen "from the inside") -

What's the meaning of meaningful? Do you mean that you literally cannot understand the opposite of simulationism? Or are using "meaningful" to mean "empirically confirmable"? The empirical indetectability of a simulation follows from simulations premises, right enough....but it cannot be used to argue for them.