Earlier quoted context omitted.
Gerrit has -2...+2. -2: This is a bad idea, don't do that -1: This is a good idea but needs improvement +1: LGTM but I don't have enough knowledge or authority to approve +2: Approved
I was in camp 'boolean', but I think this has convinced me. I always had a problem that there were developers who didn't really understand the code, but would click 'approve' anyhow because they didn't see any problems in the parts they understood. This meant that they were completely unable to actually 'approve' a review, but were only able to reject it. They were juniors, so they'd eventually get to that point, but…
Given that, what's wrong with simply commenting on the PR to document the concerns, issues, lack of knowledge, etc?
Unless you're using those +/-2 to achieve some sort of goal... but you can also do that with labels, tags, etc. on the PR.