There has been a decline in recent years but
Not a recent phenomenon
Forced on us by external factors - yet it has proven possible to generate a second crew when needed even after the formal commitment was dropped (in the same way as the MCA guys have done on occasion recently, and like the old days outside the hours when a seconds crew was required).
shortage of rear crew,
Also not a recent phenomenon. What has changed is that we now prefer to admit defeat when we run out of people, rather than doing 48 hour shifts and other work-arounds. I would suggest that the capability of a crew, at a point where some of them had been on shift for 40-45 hours, wasn't much greater than no crew at all!
reduction in training with outside agencies...
If some lifeboat units used to get an exercise a month (not something I've seen myself), then a reduction will not have hurt capability that much!