I think you might misunderstand the over-optimization issue.
Over optimization can be recognized when a certain phrase is repeated in a way that -
1. Harms the flow of the content.
2. May not harm the content flow but might create a red light for search engines.
The first one will certainly impact ranking, the second one won't impact if the content is good enough.
Content flow and over optimization:
Say, you repeat a phrase too often, something that SE recognized as your targeted keyword, and (YOU KNOW THAT) there are other ways to construct sentences without using this specific phrase, making the content rich and reachable.
Whereas, your competitors provide almost the same information without over-optimizing while yielding better user experience.
This is easy for SE to identify.