One way I see the comparison between the different media of this series is that there manga adaptation does a lot, I mean, a lot of adaptation expansion of the LN to fully flesh out everything that it becomes its own thing, petty much. The manga format probably helps a ton with how much room the series gets to breath a bit and how it matches the nature of this series that showcases sword combat and fighting.
Like all the characters beside our main characters are realized characters in their little roles in the arcs, the old maid, the androgynous assassin, the make swordsman from previous arcs, the school principal, from what I recall from the LN.