The challenge with 'semi fast' trains is that they pay little regard to the stops passengers on the train are likely to want to go to. Turning at Hooton would seem the best way to get things back on track and make sure all stops actually in Merseyside were served, but is rarely done unless the delay is caused by something South of there.
When they resort to Semi Fasts, the block is usually either an arbitrary Birkenhead Central-Hooton or Rock Ferry-Hooton. Between Birkenhead Central and Hooton. The station usage statistics show that Bebington, Rock Ferry, Port Sunlight and Bromborough are significantly busier than Eastham Rake, Spital, Green Lane* and Bromborough Rake. So potentially if the delay wasn't too bad, they could skip fewer stops and get more passengers to their destination sooner. Still not great news for
@Birkonian as Spital is one of the less busy stations unfortunately.
From a passenger perspective, cancelling one service departing Chester and everything becoming the train 15 mins later would appear better as there is something particularly annoying about your train running, but getting kicked off early/watching it sail past with people on as it is not calling at your stop which is (possibly irrationally) worse than a simple cancellation.
*Green Lane may appear quieter as a lot of trains have been skipping it due to timetabling issues recently.