SerenityOS's LadyBird browser is an impressive project, but it doesn't prove that you can rewrite something like Chromium in a few years.
It does prove you can get something working. But it will take many more years to actually get to feature parity given the long tail of web APIs. It will also take many more years to be competitive on performance with existing engines. And even if you use a memory-safe language you'll be introducing many other bugs along the way.
This doesn't diminish the LadyBird browser in any way! It can still be useful for many people in many ways.
It does prove you can get something working. But it will take many more years to actually get to feature parity given the long tail of web APIs. It will also take many more years to be competitive on performance with existing engines. And even if you use a memory-safe language you'll be introducing many other bugs along the way.
This doesn't diminish the LadyBird browser in any way! It can still be useful for many people in many ways.