You are 100% correct Mark. We can always get more specific with our selectors to target every element we want. However, I personally like to start with (near-)blank styling and target the native selectors directly, as such not having to specify tons of selectors and properties only to override the default.
The WP Customizer offers too little freedom, but at the same time, styling completely from scratch (turning off WSF skin) may be a bit too tedious for a lot of people as well. An in-between is probably what most people are looking for, so I’m excited to see what the future of WSF holds in terms of styling options. For now, I think it would make a huge difference to simply publicate the list (+ description) of native selectors (from .wsf-sections all the way down to .wsf-label, .wsf-invalid-feedback, etc.). Unless you get super fancy with your input field styles, it’s not much more effort to style the most common form properties writing custom css, compared to using a tool such as the WP Customizer.