"If AI researchers worked more closely with practicing radiologists (not academic ones) I imagine there's all sorts of areas where existing technology today can improve things."
That's almost certainly true, and surely there must be people in the medical industry already working on this. In hospitals, there are internal organisations that vaguely attempt to link up technology workers with practicing doctors to improve medicine using technology. One of my most competent former developer colleagues retrained as a doctor and worked in medical digitisation, as well as being a practicing doctor.
However:
* Often coming at a problem from another angle and ignoring existing professionals can be useful too. Existing workers are very often stuck in their ways and unwilling to accept the way they look at a problem may not be the best. I have heard from many in medicine, that doctors are extremely distrustful and hesitant towards technology, as well as fiercely protective of their jobs.
* The medical industry is internally highly dysfunctional and trying to work with practicing doctors can be extremely politically difficult. The hospital bureaucracy often actively tries to prevent practicing doctors from working directly with technologists, preferring instead to silo them and direct all communication via senior management - who are often neither technology nor medical experts. Consequently it seems more likely that major changes will come from outside.
* AI has occasionally (rarely?) shown great success in solving problems without needing domain experts. See AlphaGo.