#2: Stifling the development of young players
Throughout Mourinho's career, he has been known to use academy players sporadically and in general fails to develop them while they are still young and learning. There is absolutely no doubt that that he has the ability to extract the best out of world-class players but Arsenal currently don't have a cache of such players at the moment.
While the likes of Mesut Ozil and Pierre-Emerick Aubameyang are top class, calling them world beaters would be a stretch. What Arsenal do have is a group of budding youngsters that are consistently featuring in the first team this season.
Under Unai Emery, these youngsters are currently flourishing with the like of Gabriel Martinelli, Joe Willock and Bukayo Saka all impressing thus far. There is a high chance that a manager like Mourinho will overlook these youngsters for more proven talents and end up stifling their development in the process.