The hard question is, how could we balance a live game for 50 million players without using data as part of our process? I honestly don't know how we could feel really confident that we were making the right decisions on what to even consider adjusting.
Plus, we are making a promise to you that when you learn our game you don't have to relearn everything all the time. So tweaking live game content is something we want to be really careful about.
Conversely, when I'm tweaking new stuff here for dev playtests it's a lot more freewheeling FOR SURE. During production before launch when none of you played the game with us... that's when we went mostly on gut feel, even though we were also relying on math and spreadsheets to help with passes on TTK, etc.