I don't know about SystemD's code policies. But certainly serious vulnerabilities have been found even in C code where changes went through code review (the famous Chrome sandbox escape due to an undefined bitshift was noted to have been reviewed and explicitly "LGTMed" by two people).
And the decision about whether to code review is not necessarily static. A language that reduces the cost and/or increases the benefits of code reviews changes the decision space. And a more expressive language can free up developer time to spend on things like code review.
And the decision about whether to code review is not necessarily static. A language that reduces the cost and/or increases the benefits of code reviews changes the decision space. And a more expressive language can free up developer time to spend on things like code review.