I tend to view a history, physical exam, and lab tests/imaging as complementary aspects to a proper patient workup. To be sure, MRI has revolutionalized the field of neurology. However, we should all strive to order fewer unneeded tests, for both patients' and the health care system's sake.
In neurology, the first question you ask yourself is "where is the lesion?" The history and physical exam allows you in most cases to localize the lesion to a limited area. The next question is "what is the lesion?" MRI provides an answer in some, but not all, cases. However, simply seeing a tumor on MRI does not give you information on how the patient is doing. As you said, a patient may have a massive tumor/mets and yet show very few symptoms and signs. On the other hand, it would be important to know whether the patient is showing lateralizing or focal neurologic signs, or is experiencing features that would suggest an emergent situation. In other cases, MRI will tell you little or nothing about the diagnosis nor the patient's status.
I highly disagree with the archaic and misguided assessment that neurology is a field of diagnosis with very little treatment. Perhaps this used to be the case, but with modern treatments, there are a multitude of therapeutic options, even for the neurodegenerative diseases. Remember, neurologists also see patients with seizures, headaches, nerve palsies, meningitis, and other very treatable disorders.