Calibri font has "I" and "l" the same, according to Wikipedia. A better font should avoid characters being too similar (such as "I" and "l" and "1"). Another issue is due to the font size and font metrics, how much space it will take up on the page, to be small enough to avoid wasting paper and ink but also not too small to read. So, there are multiple issues in choosing the fonts; however, Times New Roman and Calibr…
Nothing is more inefficient than the secretary of state thinking about and conducting meetings about the font used in documents. It just doesn't matter in the sense that it "doesn't move the needle". I expect the leaders of a government deciding on matters that have a real impact on people's live, not on stuff that from a practical point of view is totally irrelevant.
The modern era we live in has far, far too much of this attitude. It's the same force eroding craftsmanship, attention to detail, and human dignity.
I find it quite reasonable for someone to care about the presentation of official government communications.
And just so we are clear, I also think Rubio is a horrible person.