I have some suggestions for https://www.whonix.org/wiki/Dev/Operating_System
The only reasoning I can find for Alpine being “secure” is that it uses PIE and SSP which every popular distro uses by default anyway making it nothing special.
“Alpine Linux was designed with security in mind. All userland binaries are compiled as Position Independent Executables (PIE) with stack smashing protection. These proactive security features prevent exploitation of entire classes of zero-day and other vulnerabilities.”
OpenBSD’s mitigations are very lacking. It doesn’t have modern mitigations such as Control-Flow Integrity (work is even being done on that in Linux). Some of its current mitigations are flawed such as its W^X which can be bypassed by using
mprotect to change a previously writable page to executable (work on this is also being done on Linux - see S.A.R.A. LSM or SELinux’s memory protections).
“OpenBSD is thought of by many security professionals as the most secure UNIX-like operating system” is also very questionable as I’ve only been seeing the opposite. For example, https://twitter.com/grsecurity/status/1211303353340366848 or https://grsecurity.net/~spender/exploits/exp_moosecox.c
Although, OpenBSD does have some great mitigations, many of these can be trivially replicated/improved on Linux. One example is Daniel Micay’s hardened_malloc which is superior to the OpenBSD malloc.
Also see, https://isopenbsdsecu.re/
FreeBSD is extremely lacking in security. It doesn’t even have ASLR by default.