The market provides a continuous and generally valid test of engineering principles. I think it's more scientific than peer review, in the most meaningful sense of the word "science".
Not all engineering is about developing products to sell to consumers. Engineers also design bridges and rockets. I don't think these are subject to the open marker in any meaningful sense.
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.