You are not limited to using defaults in your graphs. Let’s go back to the minimal theme but change the fonts a bit. I want to make the following changes:
Use Gill Sans fonts instead of the default
Increase the title font size a little bit
Decrease the X axis font size a little bit
Remove the Y axis; the subtitle makes it clear what the Y axis contains
By the time we’re through this, we have publication-quality visuals in a few dozen lines of code. I also have provided a bonus rant on Windows and R and fonts because that’s a nasty experience.