This is by now also over a decade old but still gives a much better idea how current GPUs work:
https://fgiesen.wordpress.com/2011/07/09/a-trip-through-the-...
OpenGL was always a higher level API, it just is an API that provides functionality instead of being a framework (so you had to make your own). Even in SGI hardware a lot of features were done only in software and during that time on PCs most cards could barely do more than rasterization and transformations (and some not even that).
The only HW that was truly OpenGL was Silicon Graphics IRIS workstations. IrisGL was released as open standard with some minor changed with the name OpenGL.
Also AFAIK IrisGL had functions for creating windows, etc, that didn't exist in OpenGL (GLUT was meant to bridge that gap).