How natural does (2b) sound without the nominal predicative?
(2) a. Ante Christum natum
b. Post Ciceronem consulem
If you say post Ciceronem, it simply means "after Cicero".
It could mean a number of things: After his death, after his office, behind him in a queue, after his speech…
The ambiguity is the same as in English.
It does sound natural, ...