Massively underrated by many because he might not excel outside of Liverpool, but thats a moot point. Similar to the very best water carriers like Davids, Essien, Fletcher, Park, Makalele, Kante.
He is outstanding player in the system he is asked to play in, where he concistently delivers everything that is asked of him. Lets put it another way, am not sire what other players could perform the role he does for Liverpool. Given that his team is currently the best team in the world, that makes him world class in my book.