The OP asks about 'pure' flying skills; I wonder if there is any such thing - manual flight without awareness, decision making, etc.
Also the fallacy that the use of automation 'causes' loss of skill, and that then 'causes' accidents. There is little evidence of either. Some accident reports cite loss of skill / loss of control, yet often overlook that the pilots had not understood the situation or had not been trained for such events.
Perhaps the discussion might consider:-
"Hand-eye skills (instrument scanning and manual control), if initially well learned, are reasonably well retained after prolonged use of automation.
Cognitive skills, such as navigation and failure recognition and diagnosis, are prone to forgetting and may depdend on the extent to which pilots follow along when automation is used to fly the aircraft." http://hfs.sagepub.com/content/56/8/1506.full.pdf
How can we sharpen- retain cognitive skills?