When I play Zenyatta, I tend to focus on my friends more than anyone else. That doesn't mean I don't try to heal other players, but it usually means we have a specific strategy in mind, and my friends will probably be playing characters who need to be kept alive for the team combination to work. But if you're not in my group and you're playing a Zarya, you're in luck because I will prioritize you with heals, and your targets with discord! Unless you end up sucking, then I'll just be sad.
But I also try to tell the team if I feel we need a more traditional healer, especially on KotH. Either someone in my group will play a Lucio, or I'll ask for one.