I missed your point about how he played relatively few matches, so in that light it's a lot of goals yeah.
Still, if you want to be strict about it then the ability to stay fit and to stay in the team are fairly key aptitudes that describe a WC striker, don't you think?
Not really, good stamina is an attribute that can defy a world class player, but not a good injury record. Look at Ozil, for all his talent, he fades away so quickly by the mid of the second half. World class strikers need to be great finishers, have a great movement and positioning and to be consistent, Persie got all that, and on the top of it, he's got a killer technique that most players would wish for.
Injuries and fitness can't describe a world class striker, or otherwise Ronaldo wouldn't be counted as world class from 2000 and onwards. Injuries can stop a player from fulfilling his potential, but if you are already world class, no matter how many times you get injured, as long as you can come back as strong as you were, then you are still world class.