The font size of x & y axis label & tick parameters, the line widths and the marker size might be increased; (PS: I think one typical criterion is to see if those information are clearly visible in an in-person presentation)
I think the horizontal line that marks the threshold might be referred in the legend box instead of the note section, as it is also a part of the information the figure is supposed to convey, which is opposed to the peripheral sidenote "Absence of data points...".
The color and line styles of the data might be chosen with more care for clearer presentation. For example, pseudopotentials of the same series might adopt the same/similar color family and be distinguished by different darkness or line style.
Here are my two cents on the figure:
PS: the introduction is missing here: