It might be true for Joshua, but I wouldn't be writing Fury off just yet. He only lost to an undefeated, undisputed champion, and both times by (some say controversial) decision. As painful as it is to his ego, it's not really that much of a setback to his career, provided he still wants to carry on and pursue those belts.
I have my doubts about whether Usyk will actually move back down to the cruiserweight, but if he did (for more than just one quick fight) then the door would be open for Fury to have another shot, as he's a number one contender in The Ring, WBO and WBC and number 2 contender in WBA rankings.
Maybe Usyk wants to retire as undefeated heavyweight and undefeated cruiserweight and for that he does not need to drop down a weight as he already achieved it however with cruiserweight he was undisputed champion whereas to be heavyweight undisputed champion he will have to hold the IBF belt. If Usyk wants it, he could face Dubois or Parker and if he wins then retire or go to cruiserweight with his legacy in an even better place.
I don't think it's over for AJ. One or two wins and everything changes. People were calling for Daniel Dubious to quit given he took the knee twice. Now look at him after two wins he fought AJ and now he's on top of the world but all it takes is for one loss and he'll be disregarded again. If he loses to Parker then his hype will immediately fizzle out. Same thing happened to AJ. He was on a roll battering Helenius, Wallin and Ngannou but one bad loss and people want him to retire. If AJ has another couple of good wins he'll be back with the elites. If AJ beats Fury then that puts him right back up there and whilst I think the fight is currently 50/50 I think AJ has more chance of knocking out Fury than vice-versa, especially since AJ nearly flatlined Ngannou within two rounds whereas Fury went the distance with him and was even knocked down.
I understand what you mean but if Joshua wants to be taken seriously again he must win his next fight, it really is a simple as that. The same applies to Fury and that is why it becomes an intriguing prospect if a Fury vs Joshua bout were ever to take place.
Joshua, Fury and Usyk are getting old. Dubois is 27 and Parker is 32 therefore they still have time on their side to recover from unexpected defeats but the others are in a different boat. Dubois could still be around as a professional heavyweight boxer for 7-10 years, we do not know where he will find himself in the history books.