On the other hand, simulation theory is a logical theory to rationalize the “purpose” of why we exist.
Now see. I think simulation theory is one of the possible explanations for our existence. But, I would disagree that it gives any credence to a purpose to our existence.
It also doesn't really answer the core question of how things began, it just defers them upwards to another civilisation. Unless you want to say it's simulations all the way down, there needs to be be a root real existence somewhere and there the origins pose the same questions.
I've not yet heard any explanation as to how our universe came to be that I truly believe. All explanations are problematic. But even if simulation theory were true, I'd still be bugged by the fact that we still don't get any closer to the answer of how it all began. It just explains how the universe as we know it exists.