That logic would lead one to conclude the 60 inch bucket should then be termed a “light material” bucket.I took your response and showed it to the dealer and he said you were absolutely wrong and that the buckets are made of the same gauge steel in both versions and the 60" is only rated as light duty because it is possible for you to overload the lift capacity of the loader with a full bucket. Just sayin.....
But if the material both buckets are made from is the same, and the span of one bucket is 10% more, the wider bucket is more likely to develop a smile than the narrower one. So it must be a “lighter duty” bucket, if chances are greater it will bend easier.