I'm not sure what all this 'fit for purpose' nonsense is meant to be proving.
The Pacers were built in the 1980s to deal with a very specific circumstance, the railways were in decline and many rural routes were becoming marginal. By putting together what is quite literally a bus on rails, BR were able to continue to provide services along routes which would otherwise have closed.
30 years later, the landscape is very different. Rail travel is on the up again, and we're desperately trying to make up for years of under-investment. The Pacers should have been replaced 10 years ago, but it looks like they may go on for the best part of another 10.
As for their 'suitability' for certain routes, it's quite apparent that they're running on routes far better served by other types of stock. But if that other stock isn't available, we have to make do.
If I'm on the platform at Cuddington and the train to Manchester is a 142, I'll get on it. Far better that than no train at all. Even if waiting an hour would mean a 156, I'll still take the Pacer.
On the other hand, I'd be delighted to see that route ran exclusively with 158s, or even better, electrified with a nice new-design EMU.
What's 'appropriate' for that line? Well, that depends on where you get on/off and where you're travelling from/to. It's a commuter service in the mornings, taking people from rural areas like Delamere, Cuddington, Greenbank into Chester or Northwich. It's also a rural regional service, taking about an hour to take people from the above stations to Manchester. At peak times, you'll see a pair of 150s on the route. Other times you'll get either a single 150 or 142. If you're lucky, you'll get the fabled 156. There's not really such a thing as 'appropriate' stock.
I don't like Pacers much. I think they need replaced with something better, and sooner rather than later. The reason they were built has long since expired and they're well past retirement age now. But that just isn't possible at the moment. At least the refurbished ones are clean, with comfortable-ish seating and a working toilet and they can still get you from A to B.