This is what the list of wonders look like:
| Military | National | Religious |
|---|---|---|
| Great Wall Tower | Confucian Academy | Temple of Heaven |
| Osaka Castle | Imperial Palace | Torii Gates |
| Agra Fort | Taj Mahal | The Golden Temple |
| Hwaseong Fortress | The Potala | Incomparable Monastery |
You can see each group has 1 wonder intended to be from a playable culture, plus 1 extra (Incomparable Monastery is from Myanmar).
These wonders are built (“builds slowly”), and have high powers (global gather rate, skip Fortress Age, win the game).
All these suggest they are not for the final game’s Wonder Age-up system, and not map objects to be controlled.
I believe the most likely explanation is: in BHG’s initial design for Asian civs, they simply copied the Wonder mechanic from their own Rise of Nations. That is, only 1 building of each Wonder is allowed per match, and players must race for each of them. The Wonder list is not exclusive, but shared between all Asian civs like RoN: an Indian player can build Torii Gates, and vice versa.
(Their designs do not look like they can be accessed by European and Native American civs. In the final TAD, BHG also stayed away from changing existing civs.)
This Wonder race mechanic makes intuitive sense - that’s how Wonders of the World had always worked from Civ1 to RoN.
It’s the final design of Wonders as mandatory Age-up buildings that’s an unintuitive inversion of the traditional Wonder role, and required BHG to turn the old idea on its head to invent, after their initial design had failed to work out.
(Civ3 and Civ4 introduced National Wonders, which are 1 per player but not mandatory.)