FWIW I think there is confusion in some minds. As I read the thread, the issue is not what prior experience a pilot brings to the modern long-range jet.
The issue is that a doubled-up crew flying two 15 hour sectors gives you 1 captain flying a departure; 1 captain flying an arrival: 1 F/O flying a departure; and 1 F/O flying an arrival. And all flying 30 hours.
Do that 30 times and everyone has 900 hours and 15 Departures and 15 arrivals each. Not much opportunity for manual flying, when you need to maintain autoland currency for example. That is what atrophies manual flying skills.
Chase888 in post #36 mentioned the QF HS125. Perhaps the larger airlines which fly the 777/747/A330/A380 ultra longhaul sectors, could afford to provide a programme of manual flying of small jets for their long-haul pilots, and some jet flying exposure for the chaps who "don't need flying skills". But they won't do it voluntarily, and such a proposal wouldn't be viable at all for small carriers.
I don't have an answer, but the question seems valid enough.