In a heavyweight fight anything can happen. As long as he doesn't hold back, like Joshua did against Usyk, then Wilder still has a puncher's chance. Wilder is one dimensional so if he doesn't fight like the KO machine he's been his whole career then he will not make it past the early rounds.
I don't really think that Joshua was holding back on purpose against Usyk, it is just very hard to throw punches against opponents that are always moving their head and body like Usyk did and also how Typen fury does. So as a heavy puncher like Joshua or Wilder you can not just go in and start swinging like crazy from the first minute on or you will be very tired very fast because punches that you miss are extremely exhaustive for a boxer. So you might want to wait a bit until your opponent becomes tired and slower.