Ladybird is pretty good today. A lot of web apps, even complex ones, just work. It's reached high compliance scores for web standards in a shockingly quick period. See here: https://youtu.be/VqzbqsIlaNI?si=YPdwbApq4nVYlPMQ&t=209
Seems like its easier to crack an existing browser and take away stupid features than to build one. Against TOS but I really don’t care.
Someone could try to merge e,g, V8 and Servo, once that's in decent shape. But even then it'll be time consuming to build an acceptable UI, cookie and history management, plugin interface, etc.