dozens
songwriting is debatable, different strokes etc. plus smarter songwriting doesn't mean better.
record sales... for a career which effectively spanned 3-4 years, he didn't do too badly.
showmanship, it wasn't spandex with the mic held high but there were plenty of less conventional things that happened during his brief career. plus the more conventional instrument smashing etc.
lasting effect is another rubbish one. nirvana have had plenty of lasting effect. just the bands who are influenced by them are all utterly shit and missed the point entirely. the popular ones at least.
anyway, i'm probably going to write a whole essay on this in a couple of days because as good as AIC were, nirvana were a whole other beast, and it was pretty much kurt cobains band. AIC was staley/cantrell.