For me, this issue isn't just an armchair exercise or chit-chat on the computer. I care about this issue because I have seen it and it alarms me.
I will say it one more time and then leave this to all of you to hash over. From my perspective, it isn't so much erosion of skills, rather, it is that the skills were never there in the first place. I saw pilots chosen for reasons other than aviation aptitude, placed in an intensive C172 program (and incidentally, subjected to some old school hazing), allowed to languish (often for considerable time) waiting for their slot to open, scheduled into an intensive ground school and sim program, and finally released onto the line in a right seat wide body long haul op. The opportunity on these flights to learn any real handling was non-existent. Company Manual dictated no cross wind landings and in reality they couldn't handle any, especially one that would shift during the flare. They got around all that by using the autoland feature. NO ONE did any visual approaches, hand flown or otherwise. Non-precision approaches were an emergency procedure.
The sims were every three months to the airlines credit. The FOs spent extra time, on their own, memorizing the PFD pictures for each scenario - sharing their information on a very sophisticated web site. I suppose it helped but it didn't solve the problem - they really couldn't fly very well and in their career path probably wouldn't get better.
The real solution is to put these kids in a commuter type program or even a high frequency short haul jet program and use the big jet as an upgrade. Or, dare I say, dual qualify people. (Okay, I hear the knives coming out over this...) Wash out the ones that can't hack it. This was a very real option at this particular carrier but they chose not to do it. Why? Who knows.
Sim handling sessions work okay for guys that knew how to fly once in their distant past but doesn't really do that much for clever lads that just want the expensive watch and layover entertainment.