Yea, webkit2gtk is pretty heavy (or at least it seems that way when trying to compile it), but it might have been the easiest way to render epub files as their render is pretty similar to HTML.
It's all about tradeoffs and I don't think this one is too bad. I'm glad it isn't a pure electron app.
Now we just need decent open hardware for Linux tablets! I'd love to use this program to read books on one of those mythical open source tablets that can run KDE Plasma.