Based on the lolalytics and u.gg data Nunu seems to be a a really strong champion since he has high winrates. Don't you think these buffs might put him in an overpowered state?
Possibly. The risk here is that hybrid becomes optimal and it's better than full tank is currently. Pure AP was roughly 5-6% lower in winrate than tank was in the jungle if I remember correctly so we figured there was some generous room to make it a more viable playstyle.