According to Riot, Viktor is broken too. Those nerfs hit his early game pretty hard. After being picked in the LCS, he went from being underplayed and considered 'weak' by most of the community to an OP top-tier pick. Things like that happen when the meta shifts, but now that it's shifting back to favouring assassins more, Viktor's in an even weaker spot than he was.
Don't get me wrong, he was always strong, but not nerf-worthy, and especially not the nerfs Riot gave him last patch. They hit his weakness, and not his strength. Early game, he's in a pretty bad spot, but once late game hits, he's just as strong and 'problematic' as he always was. It's delayed slightly, but the problem is still there. If Riot wanted to nerf him successfully, they should have just nerfed the damage on his Death Ray and left his Hex Core alone.