Having only one CSS/JS file is better for the loading-time of pages as it means less HTTP requests.
Having several little CSS files means development is easier. But while we create themes we focus on the general customers’ needs first, not on developers.
Anyway we have included all the CSS (legenda/css folder) and JS (legenda/js folder) files for those who want to edit them and then compile only the necessary styles in style.css file. If you are a developer you can choose what to change and what to include.
If i was a developer i wouldn’t bother you all the time. Maybe you know how to combine those files i showed you in the child theme and without me losing the changes on every udpate? I really suck at this, but i am asking you because is your theme and your coding and you know exactly what to do and where.