Watch it again, friendo.
He only 1v1'd Diana under the tower.
Then he destroyed the tower before the trio showed up.
And yeah, he was tanking the tower with 100 armor from Frozen Heart (the most armor from a single item in the game) 65 from Iceborn Gauntlet, 20 from Ninja Tabi, and 80.5 armor from Viktor's base stats at level 16. I also can't tell if he has any armor from Runes, but it is entirely possible that he has Conditioning as well.
Viktor has +4 armor per level. That is tied for the 4th most aggressive armor per level scaling of ANY champion in the game. Many of those that he is tied with are melee champions, and Bard, Nami, Anivia, Swain, Lux, and Annie are also ranged champions with the same armor scaling. He is tied with Swain for the 3rd most total armor on that list behind Bard and Nami.
So again, he has a shit load of armor. Towers don't mean much to him, .. but if he was fighting the trio under the tower he would have died.
Honestly, any tank that built this way and got this ahead of the enemy team could probably do this. He happens to have the effective health granted by the shielding in his kit and from Archangles to maximize his effectiveness against largely physical damage sources. Also his kit has great synergy with the mana and the bonus AP he is gaining from Archangles and Transcendence (I don't actually know that he has Transcendence, .. but if he doesn't, .. he's an idiot) .. He's still going to be able to dish out some damage.
Here's an idea, ... maybe you should try this and see if it is as easy as it looks.
That would actually be the best way to get Riot to nerf it.
If statistics show that a champion is dominating by being played in a way that Riot really doesn't intend for them to be played, they will nerf them for sure.