To summarize Symettra buffs:
-Left click lazor has a little more range.
-Right click charge shot goes faster.
-Can hold up 6 turrets for quick deployment now (instead of 3) and she starts with all 6. Cooldown down from 12 to 10.
-Shield gen skill removed, now you press E and she literally throws Reinhart shield flying in from of her. It has 1000hp and the energy part goes through walls. 10 sec cooldown.
-She has 2 ults now. If you press Q you switch the teleport por a Shield Generator building that gives 75 shields to all allies in a big area. It also has 50 hp/350 shields.
Found this video, watch to get an idea:
IMO she is much better to use but not really overpowered or anything. Weapon buffs means she can actually hit things now but her dps is still low. Carrying more faster turrets helps her first setup but not much on the long run. Her new flying barrier is pretty interesting but it looks too hard actually defend someone with this, it's probably more of a distraction for team fights than anything. Her new ult sounds amazing on theory, +75 shields for everyone makes a huge difference for holding the last point but on practice, it's still just like her teleporter and any gengi/tracer can flank and destroy it in 2 seconds.
But of course, a lot of casual players think she was already "overpowered" so who knows... Just reminder that all her weaknesses are still there, if someone picks symetra, just pick Pharah/Winston.
