I do believe building a new OS from scratch - taking the learnings of the past 25+ years into consideration - will lead to a better and safer OS. I mean for Linux they had to invent a lot of new concepts, replace a ton of things for security reasons, etc. It's secure NOW, and it was secure enough since its inception (I presume?), but it's the cumulative effect of years of polishing.

I mean search the kernel for references to use-after-free or null pointer dereference.

Since then, there's been big improvements in development practices, tooling, and languages to prevent security issues from occurring in the first place.