Quality player that wouldn't look out of place in Bayern, real or Barca....
He probably wouldn't look out of place at Real, because they're a bit of a mess and a mish-mash.
He'd look out of place at Barcelona, because he can't dribble past anyone, can't turn with the ball under pressure, can't keep hold of the ball, doesn't have quick feet. So he'd struggle to play the football that Barcelona play in tight areas, under serious pressure.
He'd immediately weaken the team, because he'd need extra touches, would run backwards/sideways whenever closed down, and would play too safe to occupy one of the forward positions.
Same for Bayern. He's not that good a player. Tidy, can take a set piece and can finish a move off when near the goal, but every thing in between is below 'quality'. He's ridiculously limited as soon as opposition players close him down.
He's suited to a team who don't dominate possession, because there's more space. He needs that space because he's poor at dribbling, turning and holding the ball. Countering allows him to be effective without being closed down heavily.
Think about the 'quality' players over the years - they don't need space. Mata's not quality.