Except that it cuts short their holiday by a day or whatever, if the price was right I might opt for a something like 15+ hour stopover, time for dinner, a few beers and bed in a hotel before back to the airport but what use is 4.75 or 7.75 hours, too long to sit around an airport and not long enough to go to a hotel.
As for connections via AMS to/from CWL, indeed I regularly did connections via AMS to/from BHX, I don't mind AMS so much, there is the Murphy's Irish Pub in the terminal to go for a pint of the second best black stuff and a toasted sandwich.