Wlad is a consensus top 15 ATG. If Wilder lands a freak right hand and wins an upset, where do we rank him? Top 15 too? That is one scary thought.
I don't think it's that simplistic. Firstly, Wilder's style will prove to match up favorably against Wladimir. Wilder's height, reach, and speed, punch variety, and aggressive style, will put him in a position where he can touch Wladimir unlike any opponent Wlad has faced in recent times. This could very well turn into a situation where whomever lands first wins, but at the point in time that they fight, especially as Wilder gains momentum in beating Povetkin, I favor Wilder's hunger and youth over Wlad's experience. Secondly, Wlad is not the same fighter he was. He's getting older. It happens to us all. If Wilder knocks him out, it will likely be the beginning of his reign, but imagine that he will begin to take on some of Wlad's fight characteristics as he gets older, and stop fighting as aggressively as he does now. For the time being, we should all sit back and enjoy a heavyweight killer that comes to fight.
If he beats Wlad and then goes on to do nothing significant afterwards, then he'll be remembered as somebody like the guys Ducklerr said. Not to mention the fact that Wlad is older and further removed from his prime than Lewis was. Narrative will be that he stopped a shot Wlad on a lucky punch.
There's no such thing as a lucky punch. And I don't rate current/active fighters until their body of work is complete.