It’s probably not deism, since it doesn’t require a non-involved agent, and deism does: you can posit both the simulation hypothesis and also that the universe is a game being played by some alien teenager with a sick sense of humor, or used as a car battery for an alcoholic mad scientist. This is then roughly Gnosticism and Manichean thought in a blender. (Instead of a blind watchmaker, nothing about being in a simulation prohibits a demiurge instead)

You’re right that the simulation hypothesis is equivalent to any number of previous ontological arguments, though, and you’re also right to notice how rarely that’s stated in public. I think, ironically, this is primarily because the people who are really into the simulation hypothesis are unaware of ontological arguments because they all seem to deride religion as superstition and foolishness that doesn’t need to be studied and can just be discarded.

i don’t think the simulation hypothesis is necessarily bad (i do think it’s false), except to the extent that esoteric and gnostic traditions all tend towards quietism, which i disagree with strongly. Y’all can believe whatever you want about the universe but if your beliefs lead you to ignore the troubles and joys of your neighbors, I suggest you update your priors.