Stop being retarded. I'm saying in terms of styles those two midfields are similar, which they are.
They both have a passer, Carrick/Gundogan, a ballwinner, Fellaini/Bender, and a creator, Kagawa/Gotze.
They're just not, though. Ekeke's already described how Fellaini and Bender are utterly different players. Gundogan and Carrick, meanwhile, are really only similar in the sense you mention, that they're both 'passers'. As in yes, they both pass the ball. But Carrick is an elegant, efficient distributor, preferring to stay very deep and use his superb long passes (both aerial and along the ground) to get the ball moving forwards. Gundogan is completely different, much more like Cleverley or Wilshere in style. He picks up the ball deep, but then he carries it forward personally, dribbling or setting up little 1-2s to bypass the opposition midfield.
If you actually want to find a model of what a Carrick-Fellaini midfield would look like, it would be Madrid's:
Alonso Khedira
Ozil Modric Ronaldo
Alonso and Carrick are very similar players. I can't see that there's much argument there. Khedira is stylistically a little different to Fellaini (in a midfield role - I've explained above why his 'big number 10' job is an entirely different thing) but the actual job is the same - be physical, be cynical when necessary, break up play, recycle the ball to more creative midfielders, and get in the box for set pieces.
And therein lies the problem. Even when Madrid's midfield was actually working - which arguably this season it hasn't been, at least by their standards - the combination of two deep-lying, conservative midfielders means that a creative number 10 alone, Kagawa in our team or Ozil in theirs, is not enough. Instead, they're forced to add another midfielder, a multifaceted box-to-box sort - Modric - to fill the gap. This means they have to start Ozil nominally wide, even though he still has to come central most of the time to help Modric with the creative burden.
The problem in this system is Khedira. With Alonso there, and Modric energetic and canny enough to contribute plenty defensively, Khedira's really not needed as a destroyer. But he adds so little creatively that it means Madrid effectively have to sacrifice a wing position to get another creative central player on.
What Dortmund's system actually means is that they don't make this mistake. Gundogan is a progressive box-to-box player, like Modric, equally good recycling possession on the edge of his own box, creating on the edge of the opposition's, or getting the ball from one to the other. He is effective enough defensively that he and Bender together provide the defence with decent protection. Meanwhile, he is effective enough creatively that Gotze doesn't have to single handedly link the base of midfield with the strikers and provide all the central creativity.
Yes, the Fellaini-Carrick approach would probably work. It would be 'fine'. But really, you have to lose a winger in order to make up for the lack of progression and attacking potential in the centre. Playing someone in the Gundogan/Modric mould next to Carrick would be much more balanced, creating a team that is equally strong in every sector of the midfield, and has a good balance between defensive responsibility and creativity.
That's basically my opinion, in full. I gather than we simply don't agree, and won't, so I'm just going to leave it there now.