I don't think he fits, although he is fairly similar in style to FDJ in that they are primarily ball carriers. I think in Casemiro and Fred we are international standard grafters who know how to play together when required. In Eriksen and Bruno we have specialists. We need a player who can look to displace Eriksen in time as a playmaker, playing deeper as he has been. Eriksen isn't old either.
Fred is all energy and press but no nous or ball control. He's also 30 and out of contract in the summer. Him and Casemiro supposedly know how to play together, but they currently don't whether it's for United or Brazil (Eriksen and Paqueta are preferred to him). Eriksen is a good playmaker but very often fades a bit early into games. Rabiot on the other hand strikes the balance between someone who has plenty of energy, strength and pace but is a better ball carrier, more technical and more tactically aware than Fred. He also has the height component (he is 188cm / 6" 1') which is something that is often missing from our team which plays with only 1 tall CB and Martinez. When opposing teams become desperate and start throwing balls into our box, we tend to often sub McTominay in to help in the aerial department. With Rabiot that need is diminishing.
This is my personal opinion here, but I think he's an overall better CM than Eriksen (while each has their strengths) and will indeed replace him. Eriksen is an AM who currently plays at CM for us because he's better than McFred, not because it's his best position. Which brings me to the point that Eriksen is also our only alternative to Bruno, when the latter is having one of those days where he's losing possession often and we need better control. He can't be both an option for AM and a starting CM, while also being a 30yo with a pacemaker. If Rabiot comes, Eriksen will still get plenty of games at both AM and CM when Rabiot or Bruno are unavailable or need rests.
In Rabiot we would have a player that is not going to be good enough to play as a deep playmaker, will expect to be a top earner and to start.
I don't know why people think he'd want to be a top earner. He'll likely take the overall best offer he has (taking both money and club into consideration) in the summer. We'll probably offer what we think is reasonable he might come, or not. He's unlikely to be a top earner though. People are basing it off the fact he wasn't ready to take a paycut to join us in the summer. Which is entirely reasonable from his side.
Before this summer I would have taken him. But now I don't think he improves our first 11. you don't pay disruptive players massive money to sit on the bench, we should have learned that with ronaldo. we need depth but there are smarter ways to do it - a young playmaker who can understudy to eriksen.
His mum has a gob on her and is a pain on the butt, but he himself has never been a disruptive player. If you mean about his mum, then it's understandable. She's a risk.