
De Rossi wasn't a creative coach. He was a monotonous coach who repeatedly used the same strategy and i have observed it based on the last matches
He is a young coach and does not have enough experience as a head coach so far. At Roma, he did tried to let Roma return to Mourinho tactics but their players did not play well in that match. It forced De Rossi returns back to his favorite tactics after all. He is making impression with Roma but to succeed, he needs to be flexible in tactics and if he fails, he will be like many young coaches with impression in early of career but later fail to grow up more.
There are different strategies in every match. I think De Rossi is working on different strategies. They can play against Milan with a style of play that they do not expect because Milan is analyzing them now based on the fixed tactics they play. If Rome plays with a surprise tactic, they can catch Milan off guard, but of course this tactical change has a price. If they don't play well, Milan could destroy them.
Pioli is more experienced than De Rossi as head coach and AC Milan are actually stronger than AS Roma from player resource to their performances in this season. A draw at Lecce in Serie A reveals some weakness at Roma with considerable dependence on Dybala and not too strong defense which can be exploited by AC Milan's attacking players especially Rafael Leao.
Chance for Roma and De Rossi to beat AC Milan and Pioli is not too high.