Isn’t the rename filter dependent on if the username is a complete match to a existing username. Sure, there may have been cases where the filter was glitched and disallowed a username for being too similar to another username, but in the case of Lifevault's suspected impersonator, it could’ve been that the filter was slow or unable to track any similarities between the original Lifevault account and the new impersonation one.
Obviously, as I mentioned in a previous message, they could use S:C if they think the user impersonated them in a negative way.
As previously stated, Lifevault's case is not one most of use would consider impersonation so much as mistaken identity. Also, the filter doesn't glitch to block similar names. Matching names exactly is far easier than matching similar names. So if it blocks similar names, that is intentional.
There are a lot of similar usernames. For example, in a wiki about a book or movie series, many usernames are named after the main characters. Impersionating is more than that, but each case is different.