1. Yea GR is a great relief for Mumbai, but only for those 3 days of the week. Highlighting an incident over here, when I myself was required to reach Mumbai, GR was not available on that day. Hence, I had to book a seat in HW AC from BPL to LTT. This clearly signifies that although there are more trains from JBP to Mumbai, getting reservation is not easy (disregarding those 3 GR days).
2. I remember a special was run between HBJ and Pune as well, having RSA with JBP Pune. Don't know why was it discontinued.
3....
more... 2 dailies along with several weeklies from BPL for SBC. Contrasting, JBP has 1 daily (impossible to get reservation in Sanghamitra) and few weeklies already packed from UP/ Bihar. This implies one can clearly not expect reservation on days except that of JBP YPR.
4. Delhi bound trains cannot be integrated because:
a. They do not feed JBP only, rather three different sections of MP/UP.
b. Gondwana and MPSK are 23 coachers, while Shridham is 20 and not 18 as you mentioned. Now even if you try to increase their length reducing coaches those from Mahakaushal, only 6 coaches get consumed, while 12 are still left.
.
Hence, yea, I agree that GWL does really suffer, but not BPL