World class doesn't necessarily mean perfect and for me, in this context, it relates more to talent than proven ability at the highest level.
I think Kahn is correct in his assessment that Szczesny is world class in that he has the reflexes, physique, agility and strength to make saves that look unsaveable.
Sure he will make errors because of his relative inexperience. He is still learning.
There are areas of his game that need work, but he doesn't have any faults that are unfixable or related to an inherent lack of ability.
Along with his superb shot stopping capabilities he has the qualities that are most fundamental to any world class player: absolute confidence in his own skill and the work ethic to back it up.
I guess people won't recognise that he is world class until he consistenly produces the level of performance that he produced in the German game.
Kahn might be a bit of a loon but I think it's silly to dismiss completely his views on something in which he was actively involved at the highest level for years.
I'd trust his judgement on Szczesny over anyone on here and not just because I happen to agree with him anyway 🙂