WebKit and Chromium are hard forks. The former is a fork of KHTML, and the latter is a hard fork of the former. However, in recent years I’ve only seen soft forks, and as for hard forks, I’ve only seen one with Pale Moon, which hard forked Gecko and named it Goanna due to disagreements with the direction the Mozilla Project was taking.
But why wouldn’t any organization make a hard fork, whether of WebKit, Chromium, Firefox, or another browser not based on the three mentioned above?
I don’t think that’s quite right. The Linux kernel, Firefox and Chromium all sit around 30 millions lines of code, last I checked, so if you add the rest of the operating system, it should still have more lines of code than the browser.
But yes, similar order of magnitude.