Yes, text shaping and layout are complex. My point is that the program wasn't doing anything that should have required a GPU, particularly for the resolutions that were common back then.
The promise was that WPF would use hardware-accelerated libraries such as DirectWrite to put text on the screen even faster than GDI+ (using the CPU) could do. The reality turned out to be quite different: multiple layers of abstraction and just plain inefficient WPF code [1] meant that users needed powerful CPUs and GPUs just to get reasonable performance.