Okay, I see your point. But indirection only enters the picture once you introduce the possibility of multiple graphics cards which are being communicated with

Okay, I see your point. But indirection only enters the picture once you introduce the possibility of multiple graphics cards which are being communicated with the same API—and I agree, that is an example of indirection. However, it's not the role I was attempting to highlight. I was considering the role of OpenGL/WebGL in relation to a single graphics card: if you consider that situation, the API is still necessary and what it's doing is neither (much) abstraction nor indirection. Instead, it's main task is essentially conversion: the graphics card needs data in one format, javascript programs assemble their data in another (I'm using data very loosely here; I mean to include even the program source, since it's in a 'format' we can just give directly to a GPU). That said, even something like Vulkan does abstract a bit, and once you bring in the possibility of multiple cards, the value of its role as an indirection layer becomes clear.