Subclass meant something completely different in 1E than 5E. In 1E they were basically their own class. 2E created groups with classes being a member of a group. The classes in 2E were similar to subclasses in 1E.As a point of fact in 1E Paladin, Ranger and Barbarian were all initially fighter subclasses. Late in 1E after Unearthed Arcana was published Paladin became a Cavalier subclass. Barbarian and Ranger were still fighter subclasses through the end of 1E.
In 2E Fighter, Barbarian, Ranger and Paladin were all warrior subclasses.
It was not until 3E that Paladin, Ranger and Barbarian became separate classes.