Scientifically gathered data, such as fossils and DNA analysis, is objective in that it is tangible and real. Scientists may disagree as to what it means and how to interpret it, but it exists. ID has no means of gathering data that can be measured in the real world. Therefore, all claims of ID are subjective.
Does that invalidate all other scientific theories without tangible evidence? String theory? The theory of gravity? (We still don't know what gravity is, though we can see it at work.)
Perfect. You have argued that it is not possible to develop general theories from phenomenon. That argument must also apply to the general theory of evolution. You can not allow one and dismiss the other with the same argument.
Of course, it is reasonalbe to draw theoretical inferences and theories from data. ID is precisely that. In fact, it is more. ID affirms the very collection of data because it is coherent with the act of science as rational, reasoned activity.
There is no evidence for evolution in a priori assumptions. It is, in a clearer sense than is ID, a theory.