How many people really discover new music through piracy?
Everyone I've ever known. I mostly listen to metal, which undeniably became what it is because of people mailing pirated cassettes in the early 80s. 8 of my 10 favorite bands, I discovered by finding someone with good taste on Soulseek and grabbing the stuff I'd never heard of before. Piracy is key in the spread of underground music.
Artists that sell out stadiums wouldn't be affected much, but the ones that actually need the concert income absolutely would.