Joshua and Wilder both are over rated. Joshua is too robotic and mechanical and loudmouth Wilder is wild and lacks fundamentals. That being said, last night does not negate the concept that Joshua may be the finest heavyweight of his day. Tyson losing to Buster Douglas did not decertify everything that Tyson had done up to that point. Lennox Lewis was not suddenly transformed into a bum because he lost to Oliver McCall.
In the case of Tyson, the loss to Douglas was the result of the slow erosion in focus and commitment after the death of mentor/trainer Cus D'Amato, coupled with the loss of manager Jimmy Jacobs. As well as the growing influence of Don King and turbulence with Robin Givens and her mother. The loss to Douglas was a harbinger of things to come, as he as never quite the same after that.
In the case of Lennox Lewis, he went on to avenge the loss to McCall and had a spectacular career by any measure after the loss.
I have never drank the Kool-Aid, that Joshua or Wilder were "great" heavyweight fighters. Wilder fights like a wild amateur, who happens to have the type of power to compensate for his lack of skills and fundamentals.
Neither one would have fared well against Lennox Lewis, Tyson, Riddick Bowe, or Holyfield. Larry Holmes would have crucified either one of them. Going further back, Ali, a young Foreman, and even a much shorter Joe Frazier (compared to Wilder, Joshua), would have handled either one of these very limited fighters.