Gotta say Cesc does look more comfortable, and as an attacking force we as a team look a lot better when he's playing as our no. 10. Ramires back in midfield with the license to charge forward and Cesc pulling the strings further ahead, we look pretty dangerous. If I was Mourinho I'd drop Oscar and play Cesc there with Ramires next to Matic and Willian out wide just like at Everton. And it's more flexible since we can go back into a 4-3-3 formation with Ramires playing more defensively if required, no subs needed. That's our best team, Ramires looks to have gotten over his slump last season, our best performances have come when he's been able to play with Cesc.
Oscar just hasn't been doing enough, his hasn't stepped up his game so he shouldn't play in important matches any more.