Could Dark Matter effectively falsify both Newton's concept of universal gravitation, and Einstein's theory of relativity?

Isaac Newton made two fundamental assumptions in his model of the universe. The first was that space was absolute. Effectively, modern physics has discarded this first assumption in favor of Einstein's theory of relativity. The second assumption he made was that all matter attracts other matter in direct proportion to its mass. Dark Matter has for several decades now been a speculative assumption based upon the fact that the universe does not appear to be structured quite the way it should be, presumably because large amounts of matter exist that are exerting gravitational effects, but, are otherwise invisible. However, suppose that Newton's concept of universal gravitation is false? In this case, a wide range of other possibilities would exist for these apparent gravitational anomalies. We would have to develop an entirely new concept of gravity, as a flexible force, following more complex rules than we currently understand. Not only this. We must accept that most, if not all of the proof for Einstein's theory of relativity is also based on the assumption of universal gravitation. So, all of the research supporting relativity theory would also come into question. Towards the end of the twentieth century, physicist Stephen Hawking speculated on the "end of knowledge". Other physicists developed "string theory", a theory of everything. Dark Matter might suggest that we are at the very beginning of knowledge, and that physicists know absolutely nothing!