The SprinterMeister makes a very good point about the advantages of a dedicated depot looking after a single type of unit. If Exeter can keep up 6500mpc for their 142s, or even better it, then they should be in-line for one of Roger Ford's spanners he awards each year (December/January Modern Railways) for best performing depots.
The problem is that the "bus orientated bean counters" in First 's HQ▸ (Headquarters) only look at overall costs of maintenance and small dedicated depots like Exeter are always likely to cost more per unit than large depots such as SPM▸ (St Philip's Marsh (Bristol depot)). They are incapable of working out the "value" getting more mpc in terms of goodwill and even possibly attracting more passengers when the travelling public find that their train is more likely to run and reach its destination without failing.