If skills were objective, then why do people seem unable to come together and decide what's Joe Johnson's value? Or who of Kevin Garnett and Dirk Nowitski is the best player? Or whether or not Oscar Robertson would outplay Tyreke Evans...
The skills
themselves are objective.
People unable to decide, etc.
People's opinion, etc. Are subjective.
The only argument for skills changing/subjective are Altitude effect, Aging, and Practice.
Determining Joe Johnson's value... well, Joe Johnson is more valuable in a offense that doesn't have him posting up in the paint, agree or disagree? Or where he could be more of a catch and shoot like Stojakovic, agree or disagree? Or, maybe you iso him and let him think he's Carmello, agree or disagree?
In all those situations there... Joe Johnson's skills are no different. They are the same skills Joe Johnson has period. However, you'd get 3 very different forms of production in those 3 different situations.