Unfortunately, I think that fails to satisfy the most important reason for 5e's popularity: you don't need to buy ANYTHING to play. The free download of the 5e Basic Rules is all you need to roll up a character and play.
D&D is a generalist game, not a specialist game. So it needs to have SOME core assumptions that settings can then deviate from. The question we have on our hands is how to design the core assumptions so that the game has the broadest appeal and is easiest to pick up and play.
Then they should go with a default setting for others to deviate from, because in the present form, it's the GM that must design the setting around the assumptions contained into the base books. Various testimonies here have shown that some players seem that a race that is in the PHB should be allowed and would confront GM who would forbid some of them, same with classes.
Exactly. We need SOME sort of baseline. The question at hand is how much of that baseline belongs in lineage and how much belongs in culture and if those overlap by default or otherwise.
This is a classic case of the lumper/splitter dilemma. There are benefits to both approaches, and threading the needle is really hard to do without alienating someone or making the game too complex to roll up a character and play with minimal effort.
I can see cultures treated the same by players demanding them to be included in the game. "I want to be an elf" being replaced by "I want to be from the Aerenal faction!" "There is no Aerenal in my game" "You're a railroading GM!" Striving to be generic is a worthy goal to sell books but I don't see that as the solution to the question we asked (how do we build a game that satisfies both of us at the same time?)