Is phlogiston theory so much worse than dark matter? Both are place-holders for our ignorance, but neither are completely mysterious, nor do they prevent further questions or investigation into their true nature. If people had an excellent phenomenological understanding of oxygen, but called it phlogiston and didn't know about atoms or molecules, I wouldn't discount that. Similarly, it can be very useful to use partial, vague and not-completely-satisfactory models, like dark matter.