Maybe true, however computing power has increased substantially since then. It's quite easy for them to index all the messages and search for them later, or setup alerts on key words.
However, metadata is always what it is. If you have someone who is distance 2 from 20 people who died unnaturally, but not distance 1 - that person is likely related to their untimely death.
The reason metadata is useful is because, unlike the text, it is generally required to be unobfuscated to 3rd parties for the communication to be useful to the 1st and 2nd parties.