Poorabiya Express: कोसी की शान से दिल्ली महान तक - Md Rashid Alam

Couldn't agree more, every train has a Specific Purpose with Quite Separate Passengers
1. Mumbai CSMT Nizamuddin Rajdhani is more about providing Premium Connection to Nashik and Jalgaon with Delhi (which is getting superb patronage from Mumbai itself, no surprises there).
2. LTT Nizamuddin AC Express is for Premium like travel without not so premium food or Flexi Fare (kind of a relief there 😂😂). More of a Subsidised Premium Traveling option (kind of like Garib Rath of that route with All Classes of AC, slightly higher fare and LHB Coaches)
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LTT Allahabad Duronto is the main player subsiding the immense rush to Mumbai from Prayagraj Varanasi region and a last minute fast travel option for that route (even Patna Bandra Humsafar fits that bill but the route is long and time table is slow and Patna Mumbai CSMT Suvidha is unaffordable 😂😂). Due to timings and availability it has become hot favourite of Satna Rewa Region too.
4. Nagpur Duronto is Super hit for its route and much needed last minute travel option for the people of Nagpur to Mumbai.
5. Howrah Duronto has the controlling effect over the demand for AC Class in Kolkata Mumbai Metropolitan Route, which now has support from Santragachi Pune Humsafar to be a good option for last minute Travelers.
Each Train is important for its respective route and closely following the intention behind their respective introductions. Comparison or creation of rivalry between these would be an unwise choice.