True. All passing by trains needs to be diverted via suburban stations. Earlier I thought Sangamitra would be a failure through PER. But it is not the case now.
Also, not all trains need to start from MAS. Some trains can be started from Chennai Beach too. It has longer platforms to accommodate 24 coach trains. Remember Navjeevan once started from Beach.
Also, the maintenance can be done at TBM or MS. Else the maintenance can be shifted to MDU.