I'm reasonably sure that quite a bit of the complexity is more or less directly caused by the amount of features it provides. I agree with you in that Chromium

I'm reasonably sure that quite a bit of the complexity is more or less directly caused by the amount of features it provides. I agree with you in that Chromium probably brings in a lot of features they don't need, but I would also say that reimplementing the features they do need is also a huge liability and would incur quite a bit of complexity too... but it'd make it their insular system with no other resources flowing into improving it. I don't have the data to make that call, but I would think someone at their end evaluated this quite thoroughly and determined the risks of rolling their own to exceed the risks of using Chromium. (Also they mentioned on the stream that they do in fact have a few hardware buttons for important things. Can't cite this, sorry...)