Chrome's V8 engine was actually written from scratch, unlike Webkit's JavaScriptCore (which descended from Konqueror/KJS, as you say). Google made a big deal about marketing this fact at the time. (1)
And while yes, Mozilla's Spidermonkey comes from the Netscape days, and Chakra in Edge descends from JScript in IE, plus aforementioned JavaScriptCore, each of those engines still evolved massively: most went from interpreted to LLVM-backed JITs over the years. I suspect that no more than interface bindings remain unchanged from their origins, if even. ;-)
And while yes, Mozilla's Spidermonkey comes from the Netscape days, and Chakra in Edge descends from JScript in IE, plus aforementioned JavaScriptCore, each of those engines still evolved massively: most went from interpreted to LLVM-backed JITs over the years. I suspect that no more than interface bindings remain unchanged from their origins, if even. ;-)
(1) I can't currently find the primary sources from when Chrome released on my phone, but here's a contemporary secondary one: https://www.ft.com/content/03775904-177c-11de-8c9d-0000779fd...)