Side note, but I think using LLMs like this to write PoCs in existing projects is actually a good idea to prove whatever you had in mind is feasible and worth it to pour time into. Obviously you need to not vibecode the entire thing once you're past that point though...
I think they do. Building bun is a complex task and engineers who can do that should also be able to figure out how to help out with a compiler. It is just a matter of immersing yourself in the code and be willing to put in the hours and hard work. Sure, they may not be able to help out with designing the type resolution but there is other work which needs to be done that any skilled engineer can do.