Robert Huth and Wes Morgan who were miles away from being top defenders was instrumental in a PL title, Djimi Traore won a CL for pete's sake, not sure why you are using that as a stick to say Maguire is a top defender for getting to a final.
Imagine though you pay a world record fee for a defender who can only play in a low block in a system with 6 or 7 defensive players around him, let that sink in, he'd look decent at Burnley under Dyche like Mee and Tarkowski do and how Keane also did, but put those players playing further up the field and they show their limitations, Maguire is exactly the same, now Ole has abandoned the lowblock/counter attack style and now decided to copy Pep and Klopp and failing miserably, Maguire massive limitations are for all to see, no pace, slow on the turn and poor awareness, it's why United will never ever win a PL or CL with Maguire as their main CB.