So having just purchased Substance Painter 2021, I see that this issue is still not being addressed as far as I can tell.
I am using a 2k 27" monitor, and the UI font is tiny, even with windows blurryvision settins scaling to 125%
Not too impressive considering a fix was asked for in 2014... Blender copes pretty well with any resolution or monitor size by way of a simple slider.... maybe download their source code and take a look at it?