I agree with you. If a teams gradually becomes stronger. Then it has a long shelf life. The way the Roma team has performed in the last two seasons is absolutely commendable. Their squad was not very strong. Still, they managed to perform quite well. Now if Roma management prepares a decent fund to bring in new players and strengthen the team. Then maybe next season Roma team will aim to win the title. But the problem is that Roma management is not interested in building the team by spending a lot of money.
Mourinho knew the kind of job and project Roma has before taking the job. Roma is not a rich club that can spend like the other big clubs in Europe. Mourinho knows this, so he has to work with the available. Besides, Roma still spend in their own way. They got some reinforcement for Mourinho before the the season began. Dybala and Belloti are few players Roma got to add to the squad. More players will still join but it wont be high profile players. In fact I don't think any club in Italy can buy a high profile player.
Jose Mourinho has a clear vision and mission and even though Roma is not a wealthy team that has a lot of money, so far the Roma team has improved a lot after the last 2 seasons when coached by Jose Mourinho.
but now Mourinho has been rumored to move to another team, there is a team that is eyeing him, namely PSG, I really regret it if the coach leaves because it is very likely that Rome will fall back if left by Jose Mourinho.