My hand is small and I can reach the hamburger menu. In what situation do you think you cannot reach it with one hand? You should observe those iOS/Android users how they reach, quickly and comfortably every corner of the screen with just one hand.
I don't think your thumb can only reach the lower part of the phone, unless you just do not want to move your fingers.
Again, it has proved to be working in iOS/Android. So there is no room for debate here.
So you mean iOS/Android is a total design fail? Yet many people are using iOS/Android. Why? Just for the apps? So all people are sacrificing good UI for rich of apps?
These are kind of personal tastes. For me, using squares/rectangles in all user interface is very odd. I think rounded toggles look nice. Why aren't iOS users complaining rounded toggles??? I don't agree Apple users have bad taste.
Live tiles being squares do not mean that such design apply well in every situation. Is there any design theory stating that squares and circles cannot exist together? I think Microsoft has made a wise and flexible decision here.
You should better ask some non-WP users whether they like the look & feel of Win10 or Win8.1. Most will say Win10