There really was an argument, I was there, I heard people get very angry about it. You can dismiss them as neckbeards, but the two major users of (IBM/Clone) PCs at that time were business users and computer enthusiasts of all ages, and both were hesitant to use WIMP interfaces.
The PC1512, that I mentioned, wasn't wonderful (6MHz 8086 IIRC, which while better than 4.77MHz 8088 was still hardly a speed demon), but GEM on it was smooth, more or less an equal to the Atari ST in performance. But few people touched GEM. The feeling was that GEM was easy to use but it was getting in the way.
What happened in 1990 wasn't that computers got cheap enough to tolerably run a GUI OS. Macs, Amigas, Atari STs, and GEM-running PCs predate 1990 considerably. What happened was that in 1990 IBM PC clones became available that tolerably ran a multitasking WIMP OS.