The variables are the FACTS. Weathered rims, outdoor ball compared to indoor ball (actual material alteration), wind, etc. Even in the NBA player shooting percentages alter from venue to venue gym to gym. Its not rocket science. But if you're asking for "pick-up game shooting stats" then I think we've taken this as far as we can hahaha
Stats are an average. We don't know how someone is going to shoot inside or out of a different venue. That's impossible to predict, but just based on what is projected by stats, it's MORE LIKELY that Russell Westbrook would shoot well as opposed to Allen Iverson. Those variables don't particularly refute the idea of stats being valid material to back up an argument about scoring ability.