Yup, I agree with you there - S4 is superior to T3 in so many ways. Either they stup up their game with much improved drivers or I will consider a switch to the One XL once it's released in Europe.
The thing is: it's highly doubtful that the T3 will ever get similar battery life, no matter how many updates get released and how much optimization is done. At the end of the day, it's still 2 improved, more power efficient cores vs. 4 (probably rarely used) old, inefficient cores. The only possible case where T3 could get similar battery life would be if nearly every app supported 4 cores - don't know whether that will improve in the near future.