Ah thanks for pointing that out (Lubrizol chart) . I always thought it was comparable accross the board.
I only observed that for the same brand such as Liquimoly, Ravenol, Adinol, Shell, Mannol, Castrol, etc., the API SP oil is often much cheaper than any VW 508/509 oil. But, often the pour point and viscousity index are also different.
It is possible that the extra price is caused mainly by licensing fee.
What I understand all european manufacturer oil standard are often generalized by ACEA C3, C5, C6, C7, etc.
On the other hand, Dexos 1 gen3 has tighter standard than API SP.
So, I feel like, it is still comparable accross the board but not in a proper scale.