Well, yeah, it's got to be frustrating when you can't cure something. However, many of those drugs do as they are supposed to though and improve overall quality of life and longevity. Do you think it was any less frustrating dealing with illness back before when doctors didn't have something to offer them that would likely help?
Or consider chronic illnesses that doctors can help very well. The average life expectancy of a patient with cystic fibrosis has more than doubled over just the last thirty or so years and is expected to continue to rise. Someday gene therapy may even offer a cure. A diagnoses of diabetes used to mean certain death within a few months or, at most, a couple years of diagnoses. Now doctors still can't cure diabetes, but type one diabetics have pretty much the same life expectancy as non-diabetics.
Not to mention acute illness. My grandmother came very close to dying from an ear infection as a small child and was left with permanent damage and partial hearing loss. I can not begin to imagine how much agony she must have been in. Nowadays such an infection would be nipped in the bud with a course of antibiotics.
Every day, doctors see parents who don't know if their child's ongoing or different than they have experienced before illness is something to worry about or not and reassure them that the kid just needs a little more rest and time or, less commonly but more important, finds that it is something serious and treats it. Every day doctors around the world catch cancer and other potentially deadly illnesses/conditions in the early stages when they are still treatable/survivable. Every day doctors diagnose physical abnormalities or delays in development in children at the ages where intervention can be most effective but parents may not have notice it yet.
The list could go on and on and on. The idea that all doctors have to offer are vaccines and useless drugs that cause more problems than they solve is completely absurd.