more or less the entire point of code review is to ensure that the reviewer fully understands the code that they review
i know that lots of orgs don't do it this way, but it's really important to make this point very clear: those orgs are wrong, and pathological, no matter how many of them there are
I want to agree with you. But I'd argue that for some career paths it is just impossible, and it is definitely impossible for my company. That's why I never consider myself as an engineer -- and I'm fine with it, because I don't love what I do. I take my side projects more engineer-ish.