So the final answer is:
GAMMA!You can see the edges of the letters as tiny black-to-white or white-to-black gradients, right?
And we all know what gamma 2,2 does to gradients, right?
Here are some example images to confirm that.
2.2 images were saved "just like that" from 3ds Max with gamma 2.2 - that's what you get when rendering with 3ds Max and Corona by default.
1.0 images were saved with gamma overridden from 2.2 to 1.0, which as you can see results in a linear gradient. So the tiny gradients in the letters are linear too.
Check out these comparisons:
Gamma 1.0 -
https://corona-renderer.com/comparer/8uaHMwGamma 2.2 -
https://corona-renderer.com/comparer/hEoxV6As you can clearly see, with 2.2 the white-on-black text is thicker.
As you can also clearly see, with 1.0 the letters are the same. Some monitor profiles or optical illusions may be at play here, but if you take a look at the thin lines in "h" or "w", you will definitely see it.
Extra: why did disabling anti-aliasing completely produce similar results? Because then we basically removed the tiny gradients on the edges of the letters.