It's difficult to really capture the issue using screenshots as there is no platform on which the Helix applications render in high resolution, so you have to compare it against a different app that does. The screenshot I've pasted here is a poor attempt at this. On the left side is the actually Helix editor window, on the right is a textedit window showing the same message rendered at high resolution on a Mac.
I see this problem a lot with cross-platform software. Lots of companies use Qt to deliver cross-platform compatible software, and in a lot of cases the end software is not optimized for resolution independent OS's like macOS and the latest version of Windows. As a result the software doesn't take advantage of the high resolution screens available for these platforms.
I don't know if this is a problem that endemic to Qt or not. I know the latest versions of Qt support resolution independence, but I'm guessing software developers don't want to go to the trouble of creating higher resolution graphic assets and figure that most users won't care enough about the difference to complain. For those of us who actually want to utilize our high resolution screens to their fullest potential, this is actually a fairly big issue. Whether developers like it or not, supporting high resolution screens is starting to become a buy or dont-buy decision factor.