Considering all the ones being unfairly banned since Fueygate, I would say that is high enough. Pretty much only the people that actually enjoy playing Symmetra still play her from fear of being reported on sight.
But my intention behind that “a lot” is saying its not one person or two representing the whole category, like it often is on Top 500 (one or two symmetra players only). Her pickrate in GM is not that far away from her general pickrate, so from all the people that play Symmetra, probably her distribution curve is very similar to the general public distribution curve as well.
Eg, compare that to Widowmaker. Her pickrate skyrockets from diamond and above compared to her general pickrate.