Hi
Upon browser inspection, this is what font size the section ends up showing, despite being manually set in the addon: @media (max-width: 767px) body { font-size: 13px; }
You are mistaken about this. Font size is 14px - since you tuned it in add -on. There are no hidden adjustments to the addon to which you do not have access.

To control the font size without introducing the settings on each page, remove all the font size from the addons and use CSS by placing your CSS code in custom.css file. Never edit template.css.
body {
font-size: 17px !important;
}
For general control over the headings, the same thing - delete all the values from the addons and configure all the headings through CSS.
Example
.h1, .h2, .h3, .h4, .h5, .h6, h1, h2, h3, h4, h5, h6 {
margin-top: 0;
margin-bottom: .5rem;
font-weight: 500;
line-height: 1.2;
}
h1 {
font-size: 50px;
}
h2 {
font-size: 40px;
}
h3 {
font-size: 30px;
}
h4 {
font-size: 24px;
}
h5 {
font-size: 22px;
}
h6 {
font-size: 20px;
}
In general, you can explore the code through the inspector, copy paste the entire code related to the typographic to the custom.css file and replace all with your values.