No, there is nothing wrong with it - it is perfectly understandable. Of course there is always more than one way of saying something. Another way of expressing this is "The weight of the world's annual paper production is three times that of the total vehicle production".

Not at all. To make it absolutely clear I would say: 'The amount of paper produced each year is three times the weight of the vehicles manufactured worldwide'. I've used a synonym here for produced to vary the vocabulary and the passive language to make it more direct.