There are actually lot of reasons why bots in shooters don't play like humans... but that is done for design reasons rather than technical ones. Additionally, using a GA or NN isn't going to get you better results... but rather more vanilla ones. The thing that makes human play more interesting is the unpredictability. All of that unpredictability gets washed out in a derived solution such as a GA or NN. What you have in the end is simply a single algorithm no different that some sort of rule-based system like a behavior tree, expert system, utility-based system, planner, etc. The only difference was how you arrived at that single solution. (And the major weakness being that you might not be able to meaningfully tweak it later since you might not really know what any of the results "mean".) Really, all you are doing is "hoping for the best".
IADaveMark have got any research papers or books you written on the whole arguement of "rule based" vs NN/GA. It has just made my research proposal more interesting since I nolonger have to assume that GA or NN are the magic solution for everything.