Neither do switching heroes. In both cases, its the recommended thing to do, but it can go wrong anyway. Quoting Picard, “It’s possible to do nothing wrong and still fail.”
The irony here is that Hanamura is one of the top 3 maps for attack Symmetra (the other two are Volskaya and Eichenwalde).
Point A: Fill the other side of the choke with turrets. This way, you prevent the enemy team from pushing through the choke to finish people off, and flankers from jumping the window to hit the healers. After that, spam orbs through the main choke because that map is almost a guarantee that they will have a barrier or two trying to force the game into a shield war. The orb piercing through the shields force them to move out of the way, and let you farm your ultimate.
Once you get your ult charged, place the shield generator inside the lamen shop, and let the enemy team see you doing that. The thing is, the SG is so close to the choke that most often than not, someone will try to make a run to break it. Because you turreted the other side of the choke, this can lead to an easy pick, and you can easily push after that, taking advantage of the extra health and spawn advantage.
Point B: You most often than not, captures point A with your ultimate charged (be it from the fight itself, or from having your SG refunded). Go with your team through the high ground, and helps them take control of the high ground (short battlefield, easy to enter the chaos and microwave people with your team going together). Once everyone drops to the point, turret the stair access and place your TP on top. Drop down, and help clear the point. If the enemy go to your TP, that means less bodies stalling the point. If they don’t, you basically nullified the spawn advantage. After 3 TP charges are used, you can use the refreshed turrets to scatter then through the point to make it even harder for the enemy to stall on the point, since by there, your TP already paid its dues, so losing it isn’t a big deal anymore.
If the defense have a decent Tracer or Genji, you can also opt to place a shield generator in the house from the left side of the mega before the main gate. More often than not, they will search for your ultimate to break it, and since that room only have two entrances, you can keep that enemy busy for a solid minute if you are smart with your turrets and orbs. In the meantime, your team is fighting 5v5, but they have +375 HP, and the enemy is missing a major DPS to help get rid of all that extra health.
The best part of this plan is, as you might have noticed, It do not require anyone else in the team to do anything special. No “playing around” Sym, no “required pick” to complement her plan. Just that they are consistently trying to take the point. Ie, playing the game.