Ever is a very long time, and I do not agree with that statement. There are many things we take for granted today that we had no knowledge of just a few hundred years ago. What I DO know is that science will never be able to prove the existence of something that does not exist in the physical universe. And science has proved time and again that it can discover that we would would have dismissed as impossible.
What you are doing, with all due respect, is exactly what the Trumpers do. 'The election was stolen, but it is not provable because of a vast conspiracy to hide the truth'. That is a false assumption which is used to explain their lack of proof. You are using the 'something had to exist outside of space and time'. I reject that. Just because you and I cannot imagine something other than that, it doesn't mean it's impossible.
What you are doing differently than RD is claiming that a prime mover IS necessary (or to be fair, that something had to have existed outside of space and time). I reject that. I will trust that science can, given enough time and enough technological advancement, make that determination. Because it is beyond our imagination, that does not make it impossible. And once we understand it, it will almost certainly obey the immutable laws that we know exist.
If the prime mover turns out to be a middle school kid in another universe who is playing with his chemistry set, then that is a natural occurrence. And that middle school kid did not exist outside of space and time. Only outside of space and time as we currently understand them.