Before the first major commercial GPU (NVidia’s GeForce 256 in 1999), graphics processing was handled by graphics accelerators or video cards, which had limited functionality and primarily assisted with 2D rendering tasks. Early computers often used framebuffers and simple video adapters to display basic graphics. Complex tasks were often handled by CPU.

It is true that everything exists on a gradient, but for practical purposes we have to draw the line somewhere and it seems reasonable to me to draw it roughly here.