The C4 pathway is certainly more efficient than the C3 pathway in carbon fixation. The enzyme responsible is RUBISCO (Ribulose 1, 5- bisphosphate). In C3 plants, carbon dioxide and oxygen is both present. Maximum of this enzyme is carboxylated whereas some RUBISCO is oxygenated too. So, it requires the process of photorespiration which is a waste. In C4 plants, the inner cells get only carbon dioxide in the form of malate. This avoids the oxygenation process and, hence, makes this pathway more efficient.
Kranz anatomy is not seen in CAM plants because the stomata in the leaves remain shut during the day to reduce evaporation and transpiration, but open at night to collect CO2 which is vice-versa in the case of C4 plants. As we know photosynthesis processes of C4 plants are divided between mesophyll and bundle sheath cells.