You're not wrong. Personally, I just used GitHub's web UI to preview my PRs, but I suppose having a local GUI makes it easier to amend commits and not have to force push changes.
Electron apps eat my ram and web UIs run like shit when backed by a large private instance.
It was mentioned elsewhere but you might find Sublime Merge to be useful; it's not based on Electron, it's very fast, and it makes working with various git workflows a lot nicer (to me, at least).
You can use `git difftool` to view the diff in your tool of choice (including gui editors).
I've found piping the output of git diff to my editor makes it much easier to browse compared to using the UI. For instance, searching for a particular file or line of code it much easier in the editor compared to the browser.