Compare results achieved by Mourinho and De Rossi, it's unfair to sack Mourinho and hired De Rossi then end the last season with worse result than with Mourinho in two season ago. In money spent for transfers, it's more unfair between Mourinho and De Rossi.
I really don't know what's happening in Roma recent months and why they decided to take risk and spend too much money for transfers like this. In the last months of past season, there was rumor that they considered to sell their captain player for finance improvement. Now, in this summer, things changed considerably and they did not sell players to get money but actually have net positive transfers with many big transfers.
While I agree that De Rossi started awesome, but he did not finish well. If you check his first 10 games at Roma, you will think that De Rossi was a much better manager at Roma than what Mourinho did, it looked like they were going great and then they started to be even worse, so the return became not that great.
This of course is not something that we should be all expecting De Rossi to do bad or good this season, just wait and see. Mourinho was fine, but Roma basically said if they are going to pay that much for a manager, that manager might as well take them to UCL or at least somewhere decent, and Roma did terribly at the league with Mourinho, yes they won conference and finalist at Europa, but both years sucked at league, which meant not so good for them.
Actually when Daniele De Rossi became Roma's manager he was initially doing well for the club of which most football analyst were applauding his managerial experience than that of Jose Mourinho but at some point he loss focus and Roma Began to underperform.
Jose Mourinho was doing bad for Roma as at the time Daniele De Rossi was hired and the club's management just feel they are paying Jose Mourinho too high when they can't even get to the Champions League but the club should have understood that before they can reach the Champions League it will requires them to make some sacrifices and and even though Jose Mourinho didn't achieve more for the club but they should have given him some consideration for winning the Europa conference league after going 14 years without a trophy and I believe that had it been Jose Mourinho was left to continue he would probably take the club to the Champions League.
Of a truth Roma did terribly under Jose Mourinho because as at the time of his departure the club was not doing fine i could remember. For Daniele De Rossi he needs to be more focused this season so that he can possibly take Roma to the Champions League.