On the ego-effect, I sometimes feel like cataloguing some PR-review quirks that are mostly caused by humans being humans:

1. Smaller PRs (that can be easily read) tend to receive more comments and nitpicks than a large change since it's easier for us to have all the PR context in our heads at the same time.

2. Most people are ego-tied to their code even if they pretend that they are impartial

3. Social dynamics around merging and reviewing code between senior/junior and older/newer employees

4. probably many more