When you increase the gpu power based on older tech in order to push all those pixels your going to have more heat and power draw. Apple's approach was lazy. They used more gpu's to get the some performance, used a bigger battery which takes much longer to charge, the body is thicker and then you have the heat. Heat generation is never good for electronics. Apple traded 1 positive for 3 negatives.
Correct way to attack the problem is to use a redesigned energy efficient cpu and a new gpu that can handle that resolution while keeping the same battery.
They are probably saving that for the next ipad!