"AI will cure X" is equivalent to "Human intelligence will cure X", except that we expect AI to get there first because it's denser and can be replicated orders of magnitude more quickly and cheaply. You can levy a couple of counterpoints- that humans will never cure cancer either or that this kind of AI is impossible- but those are magical pessimism moreso than the alternative is magical optimism.
Some things AI will probably just do better, even if there aren't any paradigm-shifting breakthroughs with cures and medicines.
For example, reading an MRI or other medical scan correctly goes a long way toward curing cancer. Reading it incorrectly wastes precious time as problems are ignored or mistreated with the wrong methods. I knew someone whose bone cancer was mistreated as a rotator cuff injury for a little over a year due to the fact that an inexperienced and probably overworked doctor did not correctly identify it in the slew of tests and scans the patient had taken.
In the future, it is likely that AI will always read these scans and test results more accurately than a human physician, leading to higher remission success rates. This will happen fairly quietly and behind the scenes, even if AI doesn't invent the magic cancer pill.
> we expect AI to get there first because it's denser and can be replicated orders of magnitude more quickly and cheaply
There is no evidence that AI that's useful enough to help make research breakthroughs can be replicated orders of magnitude more quickly and cheaply. Whilst that's a true fact about software, AI is not just software -- it requires a lot of hardware. And currently it's far less efficient at using that hardware for general purpose problem solving than humans are.
