Just to be sure you are aware: I don’t have ‘fat fingers’, either!
True I do often use thumb, very successfully on almost everything, but I especially tried with smaller fingers on this Font Sizing thing, and hitting the intended button consistently was just impossible.
Which you have to do, to run up (or down) the size just now, one point at a time…
If you tap and hold you should get a reasonable gradient of change, to allow small, medium and large scale adjustments without too much hassle. The buttons definitely were not designed to be repeatedly tapped upon.
A little more in the Jedi-Apple-especially-iOS style, where the Force must be with you to find.
I could still use the not-pressure-but-rate buttons to be a little more spaced out, if somehow mashing on them seems more accurately sensed than tapping. And it may be so; probably BB-8 knows. if not cento-genarian Chewie (notice how they whitewashed that?)…
I do think the saving of us all is going to be pre-prepared Styles from our laptops. I think I got that started from my Win10, if it’s not just Mac as yet, too busy now to monkey with it but using iOS Scrivener surprisingly in that. I did for certain get fonts installed.
Why is iOS version seeing such use? Because even fast thumb-typing has that mood like pen or old typewriters, where you can smoothly think and imagine between the letters, the keys.