Leon has the same ashollish personality of Kazuma but, Kazuma works because Konosuba itself is a wacky comedy. Leon has the same snark and assholish personality of Kazuma but it doesn't bit work in this type of story, sure he can be entertaining but it can be annoying because of his mentality. He still thinks that he Mob, when usually Mobs don't have stand out personality like the main character, he still hasn't come to realization that ever since he got Luxion things has changed he and Marie already changed the scripted events but he changed it the most by basically defeating the capture targets, capturing the hearts of both Livia,Angie and Clarice. He doesn't use Luxion to it full capacity because he just wants it easy and not realizing that his logic on criticizing him helps him both mentally and spiritually he still acts as 16 year old while mentally he should around his mid to last 20s.
He still has the this shut in personality because of his experience in his past life, parents were strict on him preferring his younger sister, his sister was basically blackmailing to finish the otome game which mind you he finished it out obligation he didn't care about the game or it hidden lore and other secrets,he was just finishing it so he can get out of his system remember he had to use paid to win items. And lastly his personality is basically a realistic take on the Japanese shut in, were basically Japanese people closed of themselves from the harshness of society, he became an salaryman which in Japan means you are basically a loser ,a failure to your family and it doesn't matter if the pays is good the salarymen to many Japanese eyes it means you basically you are just a person who doesn't want achieve big things, while the negative stigma of the salaryman is slowing dying, many Asian countries like China,Japan and Korea have this Honor culture that they take it seriously, image is means everything in asian society if you are not part of society you are either a laughing stock or just bring shame to your family, Japanese society has high emphasis on family or other social group because if not you are bringing shame to them and lose being part of society.
Sorry if this is long but Leon is one of the few LN character that basically portrays a real life Japanese person on a isekai world he can frustrating but the other characters makes up this novel.