This is an arbitrary distinction in the first place. You can absolutely have a relational database that only allows 0 and 1 as valid values and requires you to build integers up yourself using relational techniques. The relational model itself doesn't care what "values" are.
In practice, simple value tuples make things much more convenient, and the edge cases are minimal. You don't have to allow full-fledged composition like nested tables etc.
> The relational model itself doesn't care what "values" are.
Maybe I misunderstand what you are arguing, but the relational model is defined in terms of values, sets, and domains (data types), but of course the domains chosen for a particular database schema depends on the business requirements.
In practice, simple value tuples make things much more convenient, and the edge cases are minimal. You don't have to allow full-fledged composition like nested tables etc.