Q: +90% bonus AD
W: +80% AP
E: +100% bonus AD
R: +200% bonus AD
And the last time he got a significant nerf was in patch 4.13, back when Sona was reworked last year. His W's shield duration was reduced from 4 seconds to 2 seconds.
Is he another beloved champion of RIOT's developers, like Thresh, so they don't touch him? I swear favoritism is making this game un-fun with some champions.