The unity of gravitational and inertial mass is a core principle of the theory of relativity, which has been confirmed again and again during the last 100 years.
Sure, new hypotheses are often met with scepticism, but when there is enough evidence, they are eventually adopted. Ironically, people arguing in favor of “alternative” science and against relativity (or quantum mechanics) seem to forget that these theories were first met with the same scepticism, not too long ago, but they passed the tests and prevailed. Time will tell if quantized inertia will do the same, but I wouldn’t bet my money on it.
As for dark matter, I’m by no means an expert, but we already know particles that are influenced by some of the four fundamental forces, but not by others. For example protons interact via the strong force, weak force, electromagnetism and gravity, whereas neutrinos only interact via the weak force and gravity. It doesn’t seem completely implausible to me that there might be a particle that only interacts via gravity, which is exactly what dark matter seems to do.
However, there is one field where I would agree that it’s in a dead end and that is string theory. So far, none of its big predictions came true, but it seems almost too big to admit this and start over, as so many people have already put so much work into it. Instead, they are turning it from a theory of everything to a theory of anything, which is ultimately a theory of nothing.