I will tell you that I expected more from Roma in the match with Juventus, which lost a lot of main squard players due to injuries. But despite this, Juventus looked better and could even count on winning the match. Many said that the transfer of Dybala is an effort for Roma, in fact he cannot do anything on the field, maybe Juventus did right, that did not want to raise his salary. 
Now we still need Milan to lose points in the next matches and none of the leaders go into the gap, all for the sake of interige. 
Yes Juventus has close to seven injured players and almost all of them would not recover until September and October respectively. But Juventus is a big team with a lot of talented and experience players that can be able to at least get some good result until the team becomes complete. But in that match against Roma, Juventus was a better side. They even had one of their goals canceled due to VAR decisions. Now we still need Milan to lose points in the next matches and none of the leaders go into the gap, all for the sake of interige. It would be quite unfair to rate Dybala based on his performance against his former club, the season is just starting. Hence, he needs more time to justify the trust Roma has in him.
Juventus have a busy schedule in September. In Serie A, they have a number of crucial matches, and dropping points in these will see them fall far behind in the title race. Juventus also have two important matches against PSG and Benfica in the Champions League. As many players are still injured in Juventus. So I don't think Juventus will be able to stabilize very soon. We will see unstable and erratic performances from Juventus in the coming months as well.
Dybala is a talented player indeed. But there is no reason to think he will score regularly. He was never a regular scorer or matchmaker. But he can perform well in important matches. I think Dybala's performance will improve a bit more with Mourinho.