Hallam Line- following on from what
@tbtc said
I'd tolerate losing one of the Northern semi-fasts, only if the current stopper had the 'Castleford detour' removed. That way you'd free up paths and units per hour but not really damage the overall service too much. You could probably then use one of the saved units to provide a Leeds-Castleford shuttle if desired and still have saved units overall.
However, I don't think slashing the Hallam line services is the best idea considering the service had only just about become decent pre-Covid and it's probably wise to see how quickly the passengers return before making hasty decisions on a line served primarily by 2 car DMU's.