Of course we can't simulate the universe (or, well, a slice of a universe which obeys the same laws as ours) right now, but we're discussing whether it's possible in principle or not.
I don't understand what fundamental difference you see between a thing governed by a set of mathematical laws and an implementation of a simulation which follows the same mathematical laws. Why would intelligence be possible in the former but fundamentally impossible in the latter, aside from precision limitations?
FWIW, nothing I've said assumes that the universe is a simulation, and I don't personally believe it is.
> a thing governed by a set of mathematical laws
Again, you're mistaking the thing for the tool we use to describe the thing.
> aside from precision limitations
It's not only about precision. There are things we don't know.
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I think the universe always obeys rules for everything, but it's an educated guess. There could be rules we don't yet understand and are outside of what mathematics and physics can know. Again, there are many things we don't know. "We'll get there" is only good enough when we get there.
The difference is subtle. I require proof, you seem to be ok with not having it.