Reddit doesn't (at least as far as I know) store a history of edits, so what is saved on the database is what your comment literally is. The reason people suggest overwriting comments is because the comment itself has value (for a variety of reasons), so overwriting the comment with something valueless (in the sense that it has no value for Reddit) is better, so the database itself is updated with that valueless comment.
After that whatever you do with the account is up to you.
Right there is inherent inertial momentum with upvotes.
I'm still on the fence, because understandably the potential (and actual) for abuse makes downvotes very unproductive as a feature, but there are also situations where they are very powerful.
It takes significantly more effort to refute a wrong position than it takes to make it. Downvotes serve as an explicit balancing point against that in ways that a well written response does not. Additionally, nested comments usually get less upvotes than their parent comments.
It is what it is I guess.