> physcists would suddenly discover that spacetime isn't as quantized as they initially thought

I don't think the majority of physicists think that spacetime is quantized. Sure, something is going to happen at the Planck scale but whether that's quantization of time and space is very much an open question.

Quantizing space and time would not necessarily make simulations simpler - just like quantizing forces actually turns out to probably make the simulation exponentially harder on a classical computer - quantum computers can be simulated by classical computers in exponential time with the best algorithms that we know of, though it is still possible that Polynomial algorithms could exist.

Of course, nothing at all can actually prove/disprove that we live in a simulation in the scientific sense - it's just a transcendental model for people who don't like theistic transcendental models, but no more "scientific" than "creation science" or "the gods did it" theories.

It wasn't until Columbus came along that they finally bothered to move us from the "flat" default starter server to the spherical one.