All of those share similar traits: the lines are excessively soft in many cases. They're rendered in linear space and then baked to the target gamma ramp, instead of being rendered in sigmoidal space (or some other psudeo-sharpening/pixel-aligning w/o sharpening methodology).

The font in Numbers is extremely misrendered, that's soft even for Core Text standards. Its as if it had absolutely no hinting applied, instead of the kind they use that approximates Freetype's "light" hinting.

The Terminal.app one is okay, but not amazing, as you can see slight misshapen stems, such as in the M for Makefile.

So, I'm not sure the monitor was at fault, but given the "clear and sharp" nature of OLEDs, it certainly magnified the effect.