edited to show why your thinking is so wrong on this matter, you cosistantly ignore the fact everyone is saying get two in etc strenghten as a unit and treat it like their all saying swap the two for each other mate, practically no one said that
Agreed. The bottom line is that when you sell your best players it's very hard to improve your team ... and it's even harder when you aren't getting a good value for that player. That's why we're tearing ourselves apart arguing about this ... because when it comes down to it we all (well most of us) know that selling Fellaini at the rumoured price is a mistake.
I think McCarthy is better than many give him credit for but that doesn't mean I'd sell Felli. Hot Dog is right in the sense that we'll (probably) end up weaker as a result of this deal (unless we get crazy lucky with whomever is brought in along with McCarthy).
I just don't think we have to make McCarthy out to be worse than he is just to make that point. McCarthy can be good and it can also be a bad idea to sell Fellaini (because Fellaini is very good).
You could make the argument that if we get McCarthy in (and also have Gibson of course) that makes us slightly weaker in CM for now. Then we get someone who is already better than Osman (and RM puts Osman on the bench) which could make us slightly better (or even much better) in that position. That way we might just manage to be slightly better overall (for the sake of argument ... not saying I think this).
Fairly big gamble though (for what would be a fairly small net gain) ... especially with the window getting smaller and smaller.