Science is not particularly reliable.
And yet, we have remarkable technology, and can do medical marvels.
My tentative theory is that there's a lot of knowledge that's less formal than science in engineering, manufacturing, and the practice of medicine which makes it possible to get work done, and some fairly effective methods of filtering information that comes from science.
To be fair to the medievals, they did end up inventing the clock, windmills, spectacles, wheelbarrows, the longbow, astrolabes, chainmail, etc... without the help of scientists.
Perhaps not, but the steam engine was invented by technologists without much input from academics and the first airplane was built at a time when many highly credentialed physicists were saying it was basically impossible. The "engineers just apply theories they get from scientists to concrete problems"-paradigm doesn't really fit the historical record. As often as not, the influence goes in the opposite direction.
Corrections: (1) The astrolabe was around since Hellenistic times, although the spherical astrolabe actually does date from the Middle Ages. (2) It seems likely that the spherical astrolabe was invented with input from "scientists" (natural philosophers).