Yeah, no shit. I don't think that there's anyone who can't figure that out. The problem isn't "I can't figure out how to use my phone", it's that always having to use the phone with two hands is annoying as hell. Phones shine when you can use them one handed. They suck when you have to regularly use them two handed because they are so big.

I think a lot of phone UI stuff biases for the lower half of the screen already. UI elements for picking most frequently used apps are at the bottom, controls for ending calls etc are at the bottom, keyboards are at the botton, swiping up to change apps.

Sure, but many phones are so wide that I can't reach elements at the bottom of the screen (but on the side opposite my thumb). I'm willing to not fuss about stuff all the way in the top-left corner, but I almost always have to hold my phone with two hands to use it.