1. Reviewing code is like proofreading a paper. Suggestions are welcome, but there isn't an expectation that all suggestions be followed. The author of the code makes the final decision based on their objectives.
2. A code review is a gate that is closed until all comments have been fully addressed. The author must comply to the liking of all who choose to comment, or they are not authorized to continue.
The tone of review comments will naturally follow from their understanding. Understanding #1 yields comments aimed at persuasion. (Should we, Could we, You might consider) While #2 yields more compulsory language (Change ..., You should). Or passive aggressive language that is meant to be compulsory but softened to sound less aggressive (I would, Could you, shouldn't you).
It is my opinion that understanding #1 is most appropriate. It prevents unnecessary bottlenecks and is more respectful or differing opinions. If developers are peers, than #1 is the understanding the most accurately reflects that.