In his last few seasons in the Premier League with Tottenham and Manchester United, I really doubted his quality, but at Roma, it seems Mourinho is different. Roma have been in good form since his arrival and Mourinho did an excellent job last season despite not qualifying for the Champions League. I think Roma will give Mourinho more time to get this team back on track like in 2000-2001 when they won the Scudetto. But of course that is a difficult hurdle to reach in the near future.
I don't think Mourinho is capable of delivering the Scudetto for Roma in 2-3 seasons, he needs a lot of time for that and now their run there is looking good. Only a matter of time and financial conditions that Roma have because in essence quality players will definitely be expensive.
Roma will be a big and most challenging project for Mourinho after his success in Porto. After Porto, he succeeded in other clubs but all of them are rich clubs. They have bigger budget for transfer, salary and they are richer than Roma for sure.
Now, in Roma, Mourinho has a long term project with limited resources at beginning and along the way. He is doing great last season (helped them win a first title after many years) and likely has a very good transfer season. Dybala is a big success for Roma and Mourinho as he can help them to be more powerful in attacking. To win Scudetto, Roma and Mourinho might need one more transfer season to improve their team.
If you look at the achievements of United after the dismissal of Mourinho (in 4 years 0 titles with a stronger squad), then I would not say that his work there was unsuccessful, everyone just got used to a much higher bar in his performance. Tottenham, he also initially raised almost from the bottom of the standings. Mourinho is a strong coach and now he has some opportunities at Roma (I don't think it's about scudetto) and I hope he can use them.
He helped Manchester United to win Europa League, their only title after the retirement of Sir. Alex Ferguson. He helped them to end as a runner up with limited resources.
He was right about Paul Pogba too. We all see that after a few years, without Mourinho in Old Trafford, Pogba contributed less and less for Manchester United and again he left the club as a free agent.
They failed with their plans because they put wrong belief into Pogba. Indeed, they should trust Mourinho and give him more time, not Pogba.