As a former Symmetra main, with today’s knowledge, I’d say it’s muddy. Really, really muddy.
As a whole, the concept of non-healing support have its potential. You can even argue that characters like Sombra can fit that as well, but regardless, it’s a design space that Blizzard ignored completely after they released Sombra.
At the time of the rework, I think a lot could be done to move some of Sym 2.0 power budget away from her ultimate (which was absurdly strong) and into her base kit. There are plenty of suggestions around, and every single Symmetra main I knew had their own list (here is mine).
What changed the situation as a whole was the introduction of role queue. Right now, because of how role queue works, you can’t have a non-healing support anymore, so all utility heroes are ditched in the common pit of “Damage”.
If you want to keep Role Lock around, Symmetra can’t go back to support without some kind of healing. It don’t need to be that much healing, Zenyatta don’t heal like a truck, and is a viable support for the majority of the playerbase. But nonetheless, giving her healing means she had to ditch one of her abilities. Turrets are too linked to her identity, but “turret healing” by its immobile nature would not work with the pacing of Overwatch. It would need to be something else.
She was an anti-flanker character.
You can argue for a lifetime in the forums if she did that job well or not, but that was her whole concept. She was focused in warding areas to halt the enemy push, and if you was good with your turret placements, you would make the life of enemy flankers very hard.
Overwatch community is usually very against any anti-flanker measures in the game because they think those hypermobile heroes need to be countered with "skill (ie, aim)", but hypermobility makes aiming harder by design, and the way to counter that is relying on abilities that do not rely on aiming. Ergo, turrets, traps, and attacks with a broad attack arc.
I believe the whole 3.0 rework started from the devs removing her autolock beam, and the orb was changed to give it purpose in a world where a scary beam was supposed to be used more, and then everything else changed in sequence to cover for each design space closed from there.
If she wasn’t an antiflanker hero, probably people would be ok with she being relegated to her niche status, like people are ok with Orisa and Bastion sitting down there unusable for low ranks, and barely usable in very specific situations at high ranks. But they couldn’t stand a support hero being able to shush flankers away.
For reference, Moira and Brigitte suffered similar feedback: “Too hard to kill”, “no aim no brain”, “no-skill”, “unfair” and “not fun to play against”. And they both were also designed as anti-flanker supports.