I’d argue Joshua was a top level heavy weight - both based on what has been around for the last 10 years and even going further back, given they are super heavyweights nowadays. If he wasn’t, then it begs the question of who was for the last 10 years? Klitschko, Parker, Povetkin and Pulev were the best the division have had to offer for the last decade and he beat all 4. He wasn’t as good as Fury and clearly not as good as Uysk, while I’ve always felt Wilder in his pomp would have found the winning punch, but after that he deserved recognition as being in that top rung of heavyweights.
He hasn’t been the same since the Klitschko fight, his efforts to become a smarter, all round boxer seemed to take away his offensive skills and he started to look more ordinary.
I don’t see a way back for him now. If Dubois can do that to him, there are 10 other heavyweights who could probably do the same now. He will take on the rematch I would imagine for one last pay day but I can’t think of a boxer coming back from an annihilation like that to win a second fight or even come back any stronger.