Earlier quoted context omitted.
There was a period of a century or more where steam engine design parameters were determined by experiment and gut feel. The physics of fluid dynamics required to explain why a design is optimal just did not exist yet. There's a lot of places in history where engineering far outpaced the science required to explain it.
If your design work is not based upon science and mathematics, it is not engineering. Not saying engineering is required to build or improve a product; it is not. "try this" is not engineering.
It was always engineering. You're making the assumption that their theories are not rooted in anything coherent at all, but almost always this is not the case. Usually a "what if we..." thought is based on other knowledge, and there's absolutely nothing wrong with trial and error... this is what research and experimentation, areas of science, are all about.