qmail has one of the most notoriously inscrutable codebases of all time, and it has a startlingly good track record, because there's a coherent security design behind it; the same --- to a greater extent! --- goes for OpenSSH.
There's a side of this that I agree with, however there's other sides.
The reason I've been in the code base a bunch is because I've taken on support of forks bootstrapped by others in various scenarios.
Design safety goes a fairly long way, but it's so easy to screw up patching code shaped this way. I might trust the core, but I don't trust external patches.
The problem in practice is, distros can't help themselves.
I wouldn't trust external patches to OpenSSH either.
That said, fail2ban had an RCE in the last year, so if we're considering trustworthy surfaces, I definitely agree and practice that I trust openssh a whole lot more than a lot of other software that may come up in the discussion.