Ben Simmons has not played since June 2021, and I have some doubts he will perform as before as he still has mental problems. So even if Simmons plays next season, it's unlikely that his presence on the court will improve the Nets' results in any way. In addition, there is still uncertainty about whether Irving and Durant will stay on the team or not.
You have a point here. He has played that long and it will reflect in his basketball performance next season. But if the starts to play from pre-season, he has plenty of time to get into a competitive form. If both Durant and Kyrie stays, they can carry him into the playoffs. And then he can help when he is needed the most, from playoffs onwards. But that is still a big IF since we still do not know what will happen to both Durant and Kyrie. They can be traded or not, or will they perform at the best of their ability if they stay? Too many uncertainties in the Nets roster this season.