That’s an aspect I have thought about, too. Since no one else is notified, someone with bad intentions can be quite sure the user themselves will read the message, while a public reply bumping the topic might be flagged by someone else.

I haven’t tested how muting a user interacts with boosts. If a user has already muted another user, it could either result in an unwanted notification because of the boost by the person they muted or no notification for anyone about the bad boost, so it might stay undiscovered by members who could flag it for a while.