He just took over two other managers for the season, he is the third manager of the season for Roma, and he hasn't made any transfers neither, he is just making due with whatever he is given, and that's not always a good thing, most of the time people are quite unhappy with that. So, we could assume that this could be very bad for many people and I understand why the result would be terrible for everyone as well. This isn't some magic he could do, there is no way that he can go there and on day one make them all much better, that's just not how it works at all.
This season only passed less than a half of it and Roma already changed their coach position two times, Claudio Ranieri is their third coach in this season. Any club with many changes in a coach position within a season, actually are in a big crisis and Roma currently have big troubles. It is really hard to believe that they changed too quickly only after the summer, and it's more surprising because in summer transfer season, they got many players in. In theory these players in can help them to increase their quality and competitiveness but practically they fell down considerably and unexplainably.
Most importantly, he hasn't even seen the winter transfer break yet, lets see what he is willing to do or even Roma is willing to do. If they can get some good players then we could see them get better. At the very worst case scenario, they will just stay at Serie A, not going to relegate and they are not going to end up with any European competition next season and just try again all over.
After spending a lot of money, which they refused to give Jose Mourinho in his two and a half season, I believe that Roma will not spend considerable budget for player transfers in the winter transfer market. If they can loan some players, they will do it, but purchasing new players sounds impossible.
Ranieri will have to make all of his plans to improve Roma and rescue them with players he has now.