Lovely, but you're epically missing the point. Your midfield is FINE in attack, so changing it to accommodate two ATTACKING players more comfortably is ridiculous, particularly when you take into account how much more specialised a defensive midfielder in a 4-3-3 needs to be. You can't just get away with shoving a sort-of deep midfielder into the role like you can with a 4-2-3-1. In a 4-2-3-1, they can cover for each other, make up for lapses in concentration, and defend through numbers. In a 4-3-3, you NEED a specialised defensive midfielder. It's why United don't play a 4-3-3 regularly, and City haven't been able to properly until this season with the addition of Javi Garcia. See the contrast between Madrid and Barca, the latter being able to play a 4-3-3 because of specialised DM Sergio Busquets whereas the former not being able to since Khedira isn't.
So on one hand you're lambasting people for not knowing what Marin can do, and then go on to compare him to Kalou and tell us exactly what he does?
Listen, I've actually been watching Marin for about 4-5 years now. He would NOT have been much use right then. It would've given you something different from Bertrand, but that certainly isn't necessarily a good thing.