Spending 50 million and 400K a week on Casemiro is just symptomatic of the complete dysfunction at the club. Don't care how good Casemiro has been, he's going to be required to essentially save the club's midfield on his own which is night and day to what he was required to do at Madrid. One thing to just win the ball back and pass to Modric and Kroos. Whole different thing to run the midfield, control the game and also shield the defence on your own, all at the same time.
Also, La Liga is walking pace compared to the PL. La Liga is basically exhibition pace football. How quick (both in feet and mind) will Casemiro still be as a 30 year old with a lot of miles on his body already. As great as he was defensively, he already looked like he lost steps last season and two seasons ago. Going to look even worse playing with the likes of McFred and Maguire in by far the fastest and most physical league on the planet.