As mentioned, these are coming from Searching. The queries are actually pretty simple COUNT queries. On a proper system, it should run quickly and efficiently in that manner. However, if you are doing heavy searches, there is nothing we can do to make MySQL Full Text Search more efficient. This is an internal functionality of MySQL.
Not quite sure I understand your concern there as respectively, if your MySQL server is down for these items, your community would be down as well 🙂 .