First point: Maybe if he were a young striker i'd give it some thought, but considering he'll be 30 next season theres no time to wait around for him to maybe get back to his physical prime.
Second point: Di Maria, Rooney and Mata are 3 of the best support players in the league, you could say they didn't help him enough or you could say he didn't provide them enough of an option, either way he's scored 4 goals in 26 league games with 3 of the most prolific playmakers in world football behind him.
Third point: It's been a year and he's probably worse than when he arrived.
Fourth point: He has 3 years left on his 265,000 quid a week deal. This is a guy that could have gone to about any club in the world and chose Monaco for money, do you think he's going to be taking a massive paycut? He earns nearly 100,000 quid a more than Diego Costa does a week, he earns more than 3x what Loic Remy does and nearly 3x more than Drogba did. Our highest earner currently is Hazard on around 200,000 a week. Do you think he's going to be willing to more than halve what he earns currently with 3 years left on his deal, or do you think he is worth similar wages to Eden Hazard?
Fifth point: I don't understand it, you acknowledge that Costa and Remy have been excellent but believe we need someone on massive wages to play 3rd fiddle to them? Then go onto mention their injury problems when, even with the extremely inconvenient timing of Costa and Remy being injured at the same time late this season, has made Drogba starting necessary in a mere handful of games. Could Bamford or someone else not on 12 million pounds a year not fill that role?
I have to say your lengthy post did nothing to sway me, if anything in making me look into respective wages it further convinced me what an awful all around deal this would be.