I jumped into the backseat tonight while me and the bride went putting around. I didn't notice too much difficulty getting to the brakes, even with my size 11 1/2's. I did have just a little aukwardness getting both brakes pushed hard enough to do a run up. But thats because I couldn't get my toes pointed up high enough and was hitting the rudder peddles.
The good news, I've always been able to get to the peddles when needed. Twice I've had the front seater let the plane get loose on takeoff/landing, but I could always press hard enough to get past the belt anchor and gludious maximus. So don't worry about getting snagged when going for the peddles, self preservation has a lot to do with it.
When flying the Cub with a large bottomed person, I have to keep my feet pointed straight and use my toes.
It all comes down to all airplanes (and seats) are different. None better, none worse.
nkh