Race is such an important anchor point to the world. For eg, the difference between high elves and woods elves is that these are different cultural groups in the world not just a resource for PCs or being a rare individual. Id like any race to have a sense of depth.
I agree the story of the setting must give narrative depth to a particular species or culture. Different settings will tell different stories about them.
Generally, except for a "kitchen sink" setting, only one or a few sapient species will exist in a setting.
The features of a player character and the tropes of a particular setting need to inform each other.
For eg, the difference between high elves and woods elves is that these are different cultural groups in the world not just a resource for PCs or being a rare individual. Id like any race to have a sense of depth.
Regarding the elf, I tend to focus the High culture on themes relating to sky and politicking, and Wood culture to earth and vegetation. But both are equally about fate, magic, and beauty.
I dont think I have ever seen a Sea elven culture in any D&D campaign, but I have seen nixie and noviere eladrin. In my mind all of these are narratively identical, regardless of stats. I even think twice before considering triton or merfolk as separate creatures from the other sea folk.
In any case, each setting may or may not include any of these particular cultures.
I dont see the overlap as a benefit.
Regarding the ardling and tiefling, I view the overlap of options beneficial. The tiefling can be various Types of fiend. So the player has freedom to visulize the character in different ways, with different kinds of horns or other fiendish characteristics.
Likewise, ardling with various types of celestial to choose from can give the player freedom to visualize the character, whether animalistic or human. Also, giving celestial traits like wings to the animalistic features, helps make the ardling more appealing to players who like tropes like Egyptian gods without being into "furry" per se. But ardling can be fullon furry, and like the trope of "winged catkids".
That said. Maybe the ardling and the tiefling should have a note that when choosing a specific appearance, to think about whether the character is unique or typical of a specific community, and to consult with the DM about where such a community might be and ones connection to it.