I've used Symmetra more than most people but I kind of get why Blizzard thinks were using her wrong. Even her teleport can be considered not used it's maximize potential. I've place a teleporter near a enemy spawn like on king's row but told everyone not to use it unless you have a ultimate ready for a sneak attack. The enemy team was searching for it but could never find it.
But I'll agree that she doesn't feel she should be in the healers class.
I think it's really lazy for Blizzard to just say she's a misunderstood character. Which she kinda is but not that way Blizzard thinks, but look at Winston. In the pro scene he sees lots of use, they definitely understand how to use him despite the average player thinking he may be weak, Symmetra however is the opposite. Sees very little to no use at all, and it would pretty bold to accuse people who have been playing the game since closed beta days they do not understand how to play Symmetra.
The meta reports don't provide a full picture of hero performance, but it is a clear indicator that Symmetra has some issues. If I remember correctly, Zarya was one of the heroes people did not want to play when the game started, and had a low pick rate. Now as we've seen how good she is, that kinda turned around. Zarya is usually in most comp games at a high level at least.
People are using her to utmost potential really, the kind of tactic you described doesn't really work all the time. It may catch people by surprise, but people who've had time with the game know all about the teleporter. It makes it hard to really get anything with it.
Also, it's the support class not everyone needs to heal. Symmetra really doesn't need healing to be a good support, right now she is definitely lacking though. She doesn't really even feel like a full-blown defense hero.
_/¯