I would agree that it IS reasonable. I would not agree that it is the MOST reasonable, depending how you define it and how you define your atheism.
Any logical approach to the question of whether a thing exists should not presuppose it’s existence, but rather START with the presumption of nonexistence until proof of existence is offered.
You don’t start considering whether Dragons are real by presupposing they exist until someone proves they are not. You start by assuming they are myth until evidence proves they are real.
So we start with a position that God is myth and then search for evidence of existence. And since there is LITERALLY none, we remain at our default position – assuming nonexistence.
I would argue that is MORE reasonable than agnosticism, which is largely just an admission of uncertainty. While that uncertainty is not unreasonable, I think it’s reasoning is flawed in that it didn’t START with a presumption of non-existence, and is therefore somewhat LESS reasonable (taking the ‘reason’ part literally) than atheism.