My sources have said that Scientism is the belief that Science is the ONLY way to arrive at truth and explain reality.
Well, depending on how literally you want us to read this, it is demonstrably false.
Nobody (to my knowledge) has ever claimed that science is the best way to get to truths in many different areas. Aesthetics, for example. Some may claim an ability for science to get to truths in morals and ethics, but I've never seen a compelling argument in favor of the idea, and the vast majority of those who have considered the idea have rejected it.
Most scientists, I think, would reject the notion that science has anything relevant to say about whether gods exist. The question of the existence of god is one of faith and, as such, is outside the realm of scientific inquiry.
1. Science is actually the investigation of reality via paradigmS or presuppositions. Before Darwin, Creationism-Design was the paradigm of science. After Darwin, Materialism-Naturalism has been the majority paradigm of science. Creationism-Design is now the minority paradigm of science.
2. Materialism-Naturalism DOES CLAIM to explain the supernatural. The material process of evolution eventually produced the human brain. In turn the material brain invented the idea of gods, spirits and demons (= supernatural phenomena explained).
Here, I think, you are relying on a shifting of meaning.
Science "explains" the supernatural by, in effect, showing how the same result can be achieved without appeal to the supernatural. In essence, science explains the supernatural by eliminating it. As applied to your example, science attempts to show how the idea of gods can appeal to humans even in the absence of any such being.
In addition, I think that your thesis is vulnerable to attack by pointing out that it appears you are trying to make a boogie man out of Darwinism. You are broadly correct when you point out that pre-Darwin, science was based on a creation paradigm. (BTW, I'm quite unclear exactly what you mean by paradigm. In a few places, your usage is inconsistent with any definition of the term that I've ever seen.) And, you are broadly correct when you point out that post-Darwin, science instead is empirically based and incorporates the idea of methodological naturalism. However, by saying it in the way that you do, it appears that you are attempting to lay the "blame" for this shift at the feet of Darwinism. You certainly offer no argument in support of this thesis, and it's not one that is obviously true. Instead, science gradually moved away from the idea of attributing causes to gods, replacing that with methodological naturalism, and evolution was part of that movement. But it certainly wasn't the only, or even necessarily the main, driving force. It was a realization that goddidit was unsatisfying as an explanation and useless as a basis for predictions, but that empirical investigation was superior for both purposes.
If you do intend to blame Darwin for this shift, either exclusively or primarily, you need to provide support for that claim. If you do not, you need to rework your thesis to avoid giving the impression that you are trying to blame Darwin.
Those who would sacrifice an essential liberty for a temporary security will lose both, and deserve neither. -- Benjamin Franklin
We see monsters where science shows us windmills. -- Phat