Symmetra is the only Support, though I’m not sure she SHOULD be classified as Support, without the ability to heal allies. While it’s true that healing is not a necessary tool for a hero or champion to be called a Support (look at Janna in League of Legends), the fact that the game currently has only 4 Supports means that running Symmetra and Mercy vs. Lucio and Mercy would put your team at a disadvantage due to less healing being pumped into teammates that are taking damage.
Despite her downsides, Symmetra IS almost overpowering in some situations. The best time to run Symmetra Support is at the start of a game, on defense. This is a great idea because of her Ultimate ability, Teleporter. Once Symmetra charges it, she can put a teleportation exit pad at her current location and connect it to to an entry pad at spawn. This allows teammates to come back to the scene of battle quickly after dying, making it much easier to defend the first point. After it’s taken, however, Symmetra loses much of its appeal because the sight of battle is much closer. Symmetra can also be used on attack, after the first point is taken, to once again shorten the distance you have to travel after a death to zilch. With the way her skills work, however, she’s not as effective outside the utility of her Ultimate.
Speaking of Symmetra’s abilities… Her weapon is called Photon Projector. Similar to Winston’s Tesla Cannon, it emits a short range beam that does damage. Differently from the ape, however, the beam homes in on enemies, allowing you to deal continuous damage which even increases with time. You can even run around without paying too much attention to targetting. This isn’t as good as it sounds, however, because Symmetra is still a Support, with the squishiness that comes with it. You’re not really strong enough to 1v1 damagers or tanks. Photon Projector’s secondary attack is probably the best chance Symmetra has of doing damage. By holding Right Mouse Button, you start charging an energy ball. Once it’s fully empowered, you can release it. It will move in your desired direction, damaging any enemy it clips until splashing into a wall. While this attack moves very slowly, you can do some decent damage if you keep spamming it in the heat of battle, as people can’t pay attention to everything at once.
Symmetra’s Left Shift ability, Sentry Turret, is one of the most important reasons why Symmetra is better on defense than offense. You can set up turrets around the map, which will detect enemies, letting you know where they are, deal damage automatically, and slow. Do you get it now? You can set up Turrets in advance when you’re defending, which is much harder to do on the offensive end.
Remember my reference to League of Legends champion Janna? Yeah… Turns out that Symmetra’s E can also shield allies. Imagine that 😀
As was said already, Symmetra is a niche pick because she can’t heal, which is essential for the team’s success. Despite that, it’s seeing use in competitive play situationally. When Symmetra is used, starting the map off with Lucio + Symmetra might be a great idea because his speed boost can allow her to reach battle sites faster, safely setting up turrets in advance and allowing you to have some information about your opponents’ positioning. The advantages offered by Symmetra’s sentries are much harder to take advantage of in unorganized play, however.