The Linux kernel has the best security you can get with a C based monolithic kernel in production. Vulnerabilities often get patched hours to at worst a few days after they become disclosed; Which is faster than NT & XNU which often can take from weeks to months, and even a year or more in some past cases; which makes sense because they have limited dev power while Linux is the largest collaborative project on the planet.

The new kernels simply aren't production ready except for some niche areas, while Linux is used anywhere from PC, Servers, Embedded Devices, Supercomputers, The National Space Station, to even NASA's Mars Helicopter.

The largest security problem the Linux kernel faces to date is memory unsafety mistakes, and is where Rust comes in. Rust's approach to memory safety is from what I can tell a match made in heaven for Linux kernel development and is very likely going to greatly reduce the amount of memory unsafety bugs introduced into the production code, but time will tell.

On the flip Rust in Android has had a great impact on reducing memory unsafety bugs; which is very good news and gives us measurable data on the potential impact of Rust in Linux.