In the days of NSE▸ Thames and Chiltern, Thames Trains, FGW▸ Link and I think even the early days of FGW, there was a traincrew management presence at (for example) Paddington, and it almost unheard of to cancel trains through lack of traincrew. I remember occasions when the local manager would ask traincrew the day before, or even phone them at home on the day, to work all or part of their Rest Day to cover an open turn. The local manager would always find someone to keep the service going, even if it meant tweaking the diagrams to do so.
The managers knew their staff and there was mutual trust and support, and the “small company” culture was similar to what chrisr_75 is suggesting. That local management presence has now gone, and traincrew are now just a resource (like a train or a locomotive) who – operationally at least - are managed (if that isn’t too strong a word) remotely by people who have probably never met them.
I would be very surprised if traincrew productivity has not fallen over the years.
We are still managed locally and there's still phone calls made to get work covered or diagrams tweaked. There's even bribes of 12 hours pay etc to cover jobs but at the end of the day, delays and engineering works is just too much hassle and stress on top of what we deal with during the week!!!