The problem these days is that everyone wants a standardised fleet for fairly obvious reasons, so a smaller fleet of lower output locos is hardly going to be attractive.
However, this need not have precluded a lower output diesel-electric loco being procured. Indeed, I have suggested in the past that the newer generation of locos could have utilised technology already well-known in the automotive sector by shutting down half the engine when being used on light duties. After all, a pair of Cl66s is overkill when sandwiching a pair of RHTT wagons. They could have saved fuel and been more efficiently utilised if only they could turn down the wick a bit and run within the Type 3 power bracket on half an engine as well as running as a Type 5 when hauling something a bit heavier. ETS is a bit of a problem, though. Either they all get it or none of them do. Having a small sub-class is not efficient, but then neither is specifying a system for hundreds of locos that will never be used.
But to come back on-topic, the Cl60s would make lousy passenger engines. They were designed for heavy freight such as coal, steel and aggregates, so to make them even halfway suitable for "proper" passenger work would take huge amounts of money and lots of work. And for what? There' hardly a lot of work for the remaining ETS Cl37s and Cl47s as it is, never mind the suitable Cl67s, so where's the need to spend vast sums of money on converting a heavy freight loco for passenger use?
No, these locos are either going to find some use (either here or overseas, like the Cl56s and Cl58s) or will go for dog food tins. Harsh, but that's the way of it.
O L Leigh