OpenBSD's track record is impressive but is it a significant target compared to Windows, MacOS, and Linux?
It is easy to say "only two bullets have ever penetrated my armor" when hardly anyone is shooting at you. I do not know if this is the case because I have never used OpenBSD and I do not know how widely it is used (headless servers, embedded devices, etc.).
You can read more about OBSD's security by going to https://openbsd.org then clicking the "Security" link near the top left.
ps: FreeBSD seems to have more users than OpenBSD, and NetBSD seems to have fewer users than OpenBSD.
Also I separate things by user account, so I don't do my general browsing as the same user that does my programming, which is again separate from bank access, which is separate from .... So the kernel is providing a lot of protections.
(And I usually browse without images and javascript, which is not OS-specific but a suggestion. Many things I use don't require it, and I can flip it on or configure it specifically for those that do.)
But the nice parts of ChromeOS, as far as security properties go are the way it can be "power washed" between usages. Along with a desktop Linux system that has less binaries installed at it's base than most. And things that are built in are typically built atop chrome's sandbox.
I used to joke with my friends who ran TAILS Linux that my grandma with her Chromebook had the same threat model.