It feels like a lot of this could/should be covered by linting rules. Am I the only one who runs into this?
The one exception is interesting -- it was the only place I've worked that did online code reviews rather than in-person ones.
I disliked the online reviews for a number of reasons, the second largest being that the quality of the reviews were very, very low and the comments primarily consisted of the sort that you're talking about here. I think it's because those sorts of observations and comments are quick and easy to do, and devs tend to start just going through the motions rather than actually putting attention and thought into the review.
For the record, the largest problem I had with the online version was that it omits the part where the dev walks through the code being reviewed, explaining what it all does. In my experience, that process alone provides half of the value of code reviews. I can't count the number of times that the dev (including myself) would be partway through this walkthrough and suddenly spot an issue that escaped him -- and would likely have escaped the reviewers as well.