This speed criteria should be removed completely, this is just colonial bureaucratic mindset of Indian Railways. No other railways in the world I have seen yet that uses avg speed as criteria for priority.
IMO IR trains should be now categorized as such:
1. Rajdhani (for state capital to Delhi) / Duronto (VB Sleeper rake)
2....
more... VB + Tejas + Shatabdi + AC Double Decker = Vande Bharat (T-18 Rake)
3. Express + SF + Sampark Kranti + AC Exp + AC SF = AC Exp (loco hauled)
4. Non AC Exp + Non AC SF + Antyodaya + Jan Sadharan + Amrit Bharat = Amrit Bharat (loco hauled)
5. Garib Rath + Humsafar = Economy (3A + 3E) (loco hauled)
6. Intercity + Jan Shatabdi = Intercity (unchanged)
7. Passenger + MEMU + DEMU = Vande Metro