When his hearing loss was revealed, I felt sorry for him. As a person who made a living in radio, that's the worst nightmare and I've always been very protective of my hearing.
And yeah, Rush was a huge figure in the business. AM radio was becoming increasingly irrelevant until he adapted Dr. Dean Edell's formula for syndicated radio and turned AM back into a moneymaker. The structure of his show was copied by everyone who jumped on the talk radio bandwagon because it was so effective. The hardest thing in radio is to keep listeners tuned in through commercial breaks or for longer than a few minutes and Rush was a master. His "time spent listening" numbers were through the roof.
Yet he's also a terrible person. Proudly smoking and promoting smoking has been mentioned already, there was the incessant hounding of drug addicts until it came out that he was himself abusing drugs, railing against immigrants while his extravagant lifestyle was supported by immigrant labor (IIRC also his drug habit) and of course his moral outrage over Clinton's infidelity while he himself racked up more ex wives than Trump.
I have empathy for him as a human being because I know how cancer sucks. Sympathy? I'm struggling to muster up any.