I've said it for years, Mourinho takes over good teams who are attacking well, drills their defence, buys overly defensive players or turns players defensive(Willian, Ramires, Fabregas playing way way too deep since he joined) and proceeds to ruin a team over 3-4 seasons before being pushed out when the team starts doing worse and playing incredibly awful to watch football. Literally happened at every club. He builds extremely short term success at huge consequences to the long term.
Chelsea are woeful going forwards, started half way through last year but they ground out wins, but there is a fine tipping point between being able to grind out wins when playing this poorly and just being ****. Watch and pay specific attention to the attacking movement when they reach the final third, that entire half when the ball got forward the person passing 9 out of 10 times stays where he is expecting the guy with the ball to randomly create magic on his own. The movement of the players in/around the box is non existent. The extremely few times they've played classic pass and move(between literally two players, still with everyone else static as anything) they've made chances. Hazard passing to Fabregas then made the run giving Fabregas the option to flick the ball over the top for him to run on to.
Mourinho's teams end up like this every time, a bunch of individuals upfront who don't link up well any more, teams that run out of ideas almost instantly. Playing Costa is a bad move, by all accounts due to the injury he's barely training since around October last year. Like Ledley King he's being used for games and protected outside of them. In form when he joined he was moving great, working the defence, creating space for others and linking up well but a year of being in and out of the team, little training and he looks no where near as domineering. He's still scoring just about but the performances are a fraction of what he produced in the first months of last season.
Remy/Falcao/others, classic Mourinho he doesn't rotate and those players get used so little they have no form and no confidence, Remy has gone so far backwards since joining he looks hopeless when he plays. Falcao won't recover his goal scoring touch from the bench, awful move for him. Falcao needed to go anywhere he'd get 10-15 starts in a row to regain his touch/confidence/form, he just won't get a chance at Chelsea.
Mourinho works best when taking over an ultra attacking team and blending extreme defence with a team built for offence, but 2-3 years of drilling the offence out of them and they become bland, awful, unentertaining and not very good teams.
This is all why, after deteriorating so quickly in the last several months of last season, I don't think they'll finish top two this year.