This is an interesting discussion and we appreciate the discussion on the topic.
To provide some insight to how we make decisions, we weigh a lot of factors. There is no one single thing that forces our hand with decision-making regarding the game.
I would say the three things we look to the most are:
- Player Feedback
- Our own instincts as players and designers
There isn't a formula that tells us when or how to make changes. We carefully use the three guiding categories above to help lead us to the right decision. Those three categories don't all weigh equally in every decision as well. For example, according to Statistics, Symmetra was fine and did not need to be touched at all. But our instincts and player feedback was contrary to what the stats were showing. Obviously, we made changes in spite of the statistics, not because of them.
Another example of how this works in practice is Competitive Play. Our instincts as designers tell us the most fair, most competitive and most balanced version of Competitive Play would require 6-person teams only. It's a great design.... on paper. If people were Omnics. But they aren't. And Player Feedback has overruled our instincts in this case so we allow for any group size players see fit (including solo) to queue for Competitive Play.
More often than not, we use Statistics as a guideline or a tool. Most of our decisions are based more off of Player Feedback or the OW team's instincts for gameplay. Stats are just good to tell us how far off those instincts are. Of course, if something is truly egregious in the stats, we will take a look at it more closely.
I'm over-simplifying the process here but trying to provide some insight into how decisions are made. Time, resources and technology all play a large role in this as well. But hopefully this gives a better understanding of why we do the things we do.