De Rossi managed to make Roma a better team and not boring to watch. I agree with you that Mourinho is a great manager and no one doubts it. However, I think Mourinho's tactics are less effective at the moment. I don't know whether Mourinho is not adapting to modern football or Roma does not have players who suit the style of play that Mourinho wants to implement. But the point here is that Roma must give De Rossi lots of opportunities to build a solid squad and that takes quite a long time.
Every coach has his own tactics and style in training players on any team. And so far it has also been clear that De Rossi has been able to provide what the Roma players want so that the performance of the Roma team itself also started to be a little different when De Rossi handled it. Even though Mourinho is also an experienced coach, this does not mean that the way he trains can immediately suit the existing players at Roma, so the Roma team management has to take another option by bringing De Rossi into the Roma squad.
Several people have said here before that Jose Mourinho and De Rossi have different strategic styles and this is all due to the difference in experience and age between the two coaches.
I also admit that Jose Mourinho does have more ancient tactics, while De Rossi combines both modern strategies with ancient strategies and was able to produce very perfect tactics and was able to improve Roma's performance last season.
In my opinion, De Rossi actually also benefits from Mourinho and this advantage is only that De Rossi is able to add modern strategies to the Roma formation that Mourinho has managed neatly, so that De Rossi doesn't need to make too many changes because the formation that Mourinho has previously formed is already in place very perfect, it's just that ancient strategies are a little ineffective when used in today's new era.