Hi Bryan -- Sorry that Cascade doesn't yet provide all the customization options you are looking for. We have intentionally kept options minimal to keep the authoring experience simple, but we realize some authors want more and we're monitoring feedback we receive. We haven't had many requests specifically for super/subscript formatting, but we'll consider that for a future update.
As far as the font size, there are a few font options to choose from in Settings > Appearance that have somewhat different sizes (Noto Serif is a bit larger than the other options), although I realize this is not the level of control you are looking for.
Cascade is an open source app, so this means you can download the source code, modify it to make the customizations you want (such as changing the font size throughout), and host your version of the app. This would require some basic knowledge of HTML and CSS, but here's an article that describes that process if you are interested.
Owen Evans
Lead Product Engineer | StoryMaps