ER only has to manage its own trains like Poorva, Rajdhani, Duronto, and many trains on patna, malda, njp route. ER always wanted it to be separate.And in HWH old Complex is controlled by ER, I think there is no direct line for south line and trains needed to be diverted via long route. Well you are absolutely correct about maintenance time. Around 20 hrs time is given to most of the trains you have mentioned. And if its rsa is done, can be managed very appropriately. Howrah Puri Express can easily have rsa with any of the trains you have mentioned.