If an extended multi-year period of excellent play is the qualifying metric for "world class" - then, for me, John Stones, as good as he has been last year, doesn't merit the accolade. In recent years Stones has been prone to lapses of concentration resulting in extremely costly, entirely avoidable errors; this undermined his performances to the extent that he fell out of favor and wasn't a first choice starter.
Kudo's to Stones for almost entirely eliminating these sorts of errors from his game.
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If however - the criterion for "world class" is outstanding play over the course of last season - then Stones is "world class."
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For me, the term "world class" is mostly about last season - and I would rate Stones as "world class."