The range of options that the slider offers is not equivalent to the options offered by just displaying the 5 variants - with the slider you can select a lot of values in-between variants.
Having said that, I'd prefer a keyboard-only way to do it too.
Developers also tend to spend quite a lot of time sitting at desktop-class machines with nice big monitors, because amazingly enough Emacs/IntelliJ/Visual Studio/whatever doesn't run on an iPad mini.
Having said that, I'd prefer a keyboard-only way to do it too.