The peer review process feels very mean from the reviewers perspective. I wish I could review papers during in person classes as writing criticisms comes off sort of rude whereas talking to the person is easier. Anyways, it is definitely useful to be the reviewer as you gain insight into common mistakes made and learn different revision techniques. Getting in the reviewer mindset is also useful for your own paper as I can now go back and read it objectively, judging if things truly make sense and come together well. It is easy to write something and just submit it without reading but in order to compose a properly good paper reviewing is essential.
One of the most clear lessons I gained from doing peer review is redundancy and concise writing. When doing a draft and getting your thoughts on paper a lot of fluff appears naturally. Trimming that and enhancing your actual ideas will always lead to a higher quality paper that is easier to read.