"why does he have to open with, essentially, 'The people who are actually getting things done and most excited about my platform are doing things wrong. I'm going to tell them they're doing things wrong"

He's acknowledging that these people had to do things wrong, at least in the sense that they had climb a steep learning curve and deploy a heavyweight system, because they basically had no other choice. He's describing the gap that he saw that motivated what he demonstrated. Those artists aren't going to be offended that he attacked their deep love of Unity, they're going to be happy that they have an alternative that suits their needs.