Being a glass cannon doesn’t matter when you have two tanks in your face blocking line of sight from her in some form or another, alongside having resources dumped into her.
It’s the same reason why tracer was dominant pre-brig.
A bigger reason why she might’ve been nerfed was not just because of her being a hero that absolutely dunks on lower-elo players, she was probably a very busted hero in professional scrims and in play-testing games.
Then…switch? Orisa can still use her shield from a distance and one of her complements can finish off the Symmetra. Remember that she is also useless against snipers and Pharah. It’s as if we have this thing called bunker and dive comps.
and Sigma in every round is precisely the reaosn why these nerfs should have never happened. It’s as if he was just released or something. Of course everyone will be trying him out. Why not wait until his excitement is gone before tuning Sym’s again? Where was the Mei tune? Where was the Reaper tune? These two also became more viable once 2-2-2 beta was released .
if it’s lower ranks… why didnt they nerf… the auto aim turrets…
I was referring to playing against a symmetra. She’s next to impossible to focus down, especially when barrier’s up.
She dumpsters tanks, why would any of them be an issue for her?
Well, now it is. 
Double barriers are common, her ammo replenishes whenever she hits barrier, her max damage on her beam is 195, the bug fix makes it so you’re always hitting that 195 dps without the weird cut in damage whenever you went off target, combined with the fact that because the beam is thicker and players in lower ranks will most likely panic when they start getting melted by a Sym at max damage so they either can’t react fast enough to kill her or they try to but because their aim is already off and Sym has a higher damage and thicker beam it probably made the most sense to lower the damage of the beam.
I’m by NO means saying these changes are good or that I like them. I can just see why they decided to go with these changes to her primary over turrets. If they only did this to Sym then I would say there is something else going on here but considering that Zarya literally got the same treatment with her beam being lower in damage and no longer being thicker when she’s high charge. I can only assume they did this because the beam change was having these characters pump out more damage then the devs intended them too which can be scary since before the bug fix both these characters could put out very scary damage. I’m not s fan of the reduce thickness of their beams but we’ll just have to wait and see how these changes play out. They’ve reverted changes on characters before so if the response from this is overall disapproval then they will likely tone back these recent changes or buff her somewhere else to compensate for it.
Just my two cents on these changes tho sorry for the essay response 