I don't see how it is. Different, but the same number, of elements is a different time. There's no constant time between [0, 1] and [0, 10], both having two elements.
The main "value" in the domain of sorting problems is the number of elements in your collection.
A subproblem also considers the elements to be integers, then they become another "value" domain. (But in general, sorting problems only need their elements to be comparable, not necessarily integers.)
