These are are all past achievements, I mean Xavi has won every single trophy going and he is still playing, but nobody in their right mind would still call him world class. Rooney at his peak was arguably a world class player, but these days he is nowhere near world class when you compare him to the likes of Suarez,Aguero and Lewandowkski. Maybe the problem is your definition of a world class player, because you seem to play fast and loose with this term, when in truth only the truly elite footballers who are still performing at a high level can be called world class.
Rooney has been utterly dreadful at times this season, has the touch of a donkey and can't pass for ****, Man Utd fans were begging LVG to drop Rooney and they wanted to see Martial play through the middle. From 11 league starts the bloke has scored 2 goals this season, that is dreadful. Last season he scored 12 league goals from 33 starts. World class indeed.
If I was describing Xavi's as a player of course I would use the term World Class. Even if with age he may no longer be one of the elite's.
Zidane for example will always be World Class. He has done enough to be deserving of the tag.
Also when discussing a players ability its not wise to focus purely on the present. Vardy for example is outscoring Diego Costa this term. Doesn't make him a better player.
Rooney has been poor this Season but he is clearly World Class talent. On this occasion I don't use the term lightly. ( also I don't agree with your comparisons at all considering Rooney has played as a CF/SS/WF and midfielder. When you take that into consideration 304 goals is a quality achievement.)
Rooney is one of the best players we have ever seen in the EPL. That's my honest opinion.