Not even Google started from scratch. They started from WebKit and used their billions to overhaul, maintain and change everything from the engine to the renderer.
> But maybe you don't even need to build another Chromium.
That's what Servo said years ago. I don't see the progress or hype around that anymore.
Maybe Ladybird is different, but overall I'm very skeptical; but an alternative browser that is not Firefox, Chrome or Safari needs a high multi-person and project contribution for it to work.