Now about Mueller. Firstly with all humility, I'd ask you to take back your words.
Saying he's not been a game changer and his performances this season only draw an average response from you, I've got to say man, that is just shit level above shit-crazy. You're kidding right when you say he gives the ball away too easily! Actually that'd be Robben since he goes for the tries himself and most of the times ends surrounded wasting an opportunity.
Footballing is not all about dribbles and tricks. Heck, then those street footballers could very easily own Messi/CR.
It's about the whole package you bring to the team as a footballer. There are four things I'd say that count.
1. Holding/Passing the ball
2. Creating spaces
3. Right time right place right person.
4. Fight to win
And I'd say, note this please, that creating space is far more important than holding the ball. Like you saw against Barca. They held the ball for 63% of game time but they couldn't create the space. Mueller is the best out there is when it comes to creating space, for himself and for others.
He's a brilliant reader of the game and quite uncanny and unorthodox. His control of the game is far different from Schweini's or Kroos' or Robbery's.
They control the tempo of the game, he controls the GAME. Also, the right place right time right person thingy. Nobody can argue here. He's a GOD (or maybe a 'nature-law breaker' would suffice) when it comes to this. I hope you'd have seen him pop out of nowhere many times. Just when you think if only someone could be there to receive/hit the ball, you exclaim, FK! Mueller just popped up again. I'd have said it that he makes it look almost easy and effortless but he's the guy doing maximum runs in the team, be it the 1st min or 90th.
Kroos is a unique breed of CAM but Mueller is may be one of a kind footballer. To say that this of all season's has been average, I guess you'd have to be blind or ignorant to do that. Every player is passionate and desires to win, also everyone fights to win but he is far better a fighter and more passionate than Kroos/Robben could ever have been or ever will be. It's not so much about the desire to win than the fight to win that matters in every game. He's kinda SPARTAN when it comes to these attributes.