TF2 has (or had) a concept of "place" in the form of named servers. That made it possible to encounter the same stranger repeatedly over time.
In contrast, Overwatch wants you to already know and specify your friends into their social-media graph and group up before going to a random/anonymous/ephemeral location. So you seldom knowingly encounter the same stranger twice.
> FFXIV
Thinking about an MMO, a "placeless" MMO would randomly assign you to a one of a great many small instances every time you log in. Eugh.