But yea this glosses over a bit trial-and-error designs and, so to speak, "genetic optimization" kinds of designs where we just try random stuff and say "Hey, this works. Not sure why, but it works.".
There's a lot of places in history where engineering far outpaced the science required to explain it.
Not saying engineering is required to build or improve a product; it is not.
"try this" is not engineering.
You may not have a good enough model for this observation to allow you to predict the results of other starting conditions, but it’s a model nonetheless, one that narrowly applies to the conditions you tried.
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.