I am finding that the text on the screen is either slightly too small or the color does not make the wording stand out enough
I am complaining about that since years, even when canonical was still the developer. But seems nobody cares about that.
On my BQ E4.5 is small thin grey text on grey background, without any possibility to change that system wide, like it's possible on Android.
Om the desktop version, Ubuntu put a lot of effort to be a barrier-free OS with high accessibly.
The Accessibility Team: https://wiki.ubuntu.com/Accessibility
But on the phone you are out, if you don't have perfect vision. And like you said, there are hundreds of millions of people without perfect vision.
For example, the text below the desktop-icons is very thin and small.
In Dekko the message preview. The subject of unreaded messages is visible, but when already readed, it gets grey and the preview text below the subject is grey and very thin text. For me very hard to read.
So it should not be changes in single apps, there should be a system-wide option to make all text bigger and change the text color to black with high contrast and not grey.
A setting like it's possible on Android.