It's not only about performance but also development time. Products like NVDI only had a chance, while the original VDI was already slow. But it was good enough to ship a product.
Putting a further burden on the processor with proportional fonts while increasing the development time (coping with them in the applications (resource editors, desk, tools)) made no sense from the management standpoint.
It also explains the price tag difference between the Macs and Ataris.
Having a usable graphical user interface already made a difference big enough to tickle the desire to upgrade to those machines.
PCs are even a different story while they offer very fast hardware text modes (contrary to the Atari 16/32 bit line)... ...and there were quite many window libraries/interfaces for applications for those modes.
Users wanted those interfaces but not necessarily proportional fonts.