convert luiz to striker since he likes to roam forward. then we have "defensive striker"

Imo, Mou is trying to play a high pressing game from high up the pitch. Meaning that the striker and the 3 AM needs to work and press the opposition when we don't have the ball. Something like Pochetino's tactic for S'ton. Oscar is a willing worker. Mata to be honest, is not adapted to it. Oscar and Mata both are quality players. But both with different styles. Oscar is more all round, and a runner. While Mata's quality is in his through pass, his vision, his pin point cross and superb pass.

So actually, it is a bit unfair to compare Oscar and Mata. It's just a pity that Mou's strategy is more suited to Oscar and not Mata. Sigh. Whatever Mata's decision it, I will respect it. This guy gave us 2 superb season as the player of the season. Hats off to him.

Think of it as
Oscar - Kaka (finisher)
Mata - Xavi (a Xavi playing in more forward position)

To fully get the best out of Mata, we need a top top predatory striker. Some one that plays at the lines, some one like Chicarito.