One person's poor regulation is another's good; In the OP example, passengers on the Shrewsbury starter, and joining en route, would have been pleased their train was on time, whereas those on the further delayed Holyhead train were no doubt disgruntled. The key factor should be minimising overall delay and therefore disadvantaging the least number of passengers. But it is, as I said earlier, an inexact science, and when Train A is delayed by Train B, Train A's passengers, crew, and quite often different TOC from Train B, will inevitably not be pleased. In NR Control we used to reckon that if we got a similar number of regulating complaints from all our TOCs, we were being as fair as we could to everyone!