I'm sure he's really strong in higher elo, but he's not without his weaknesses. Personally, a melee with a gapcloser, built-in sustain, and cc is a decent pick against viktor. I've played several games against him now and at least at gold elo I can tell you that GRASP renekton can 1v1 match the average gold elo viktor top. At LEAST... I've had one or two games where they've needed their jg to babysit just to prevent me snowballing on viktor and removing him completely from the game.
While higher elo players will better know how to avoid/minimize giving me advantageous trades as viktor vs renekton... viktor has no escape tools besides gravity well and running fast. So any time he shoves to your tower he's ripe for a gank by your jg. In the early game he's extremely squishy. He can't gravity field both you and your jg. So he's left a sitting duck to a well-timed gank even at higher elo.
Is he a bit more obnoxiously strong than he should probably be? Yeah. But the same can be said for stuff like sion. And there isn't nearly as much outcry against THAT. For better or worse, until they can improve viktor's ability to compete with other midlaners - which isn't happening with his w being mostly useless vs the mobility and/or range advantage other mids tend to have - he's probably here to stay in the toplane for awhile. Much like nerfs, changes, and other factors saw taliyah or graves become staple junglers rather than midlaners and adc's like they used to be. What I'm getting at is that... Riot needs to update his kit if they're going to see long term success for him as a midlaner rather than an odd new toplaner.