I mostly like playing Mercy but Lucio is pretty good too.
Zenyatta is flat out underpowered though and Symmetra, while great in her own right, is not a support. It's just gonna wind up like HotS where support quickly became healer and characters like Tassadar and Tyrande had to be readjusted to suit that.
I wonder if it's to do with the speed at which people can die and respawn in the match, but also characters like Tracer who can easily catch up to targets and finish them off.
Basically, scampering to health packs isn't as easy in this game compared to other FPS.