Neat here has the meaning of tidy and well organised. The idea in 1 is that we can't categorise people with simple definitions because people are complicated with different parts to their personality. The idea of "neat little boxes" is just a phrase used to talk about defining/labelling/categorising people and that it doesn't make sense to do so. In 2 they are saying a similar thing that because people are all different and complex that a varied approach of leadership is necessary instead of "putting people in boxes." That would be like saying "Person A is always quiet and shy so they should always be categorised with other similar people that are also quiet and shy".