Oh this is stupid.
Lamda worked with him for a month, saw him repeatedly demonstrate his skill/power including taking on the captain in a duel and yet is all "lolz my trap with basic generic bandits is going to work for sure" then tries and fails to attack single-handedly instead of doing something sneaky or trying to run or whatever.
Then Sieg gets promoted and in spite of everyone witnessing his power first-hand multiple times and knowing that he just took down a huge bandit ring they're all "this can't be, he's just a newcomer he's not good enough!"
Some of this might be poor translation because I know that KS group is notoriously inconsistent and at times lazy. but it also just feels like the original writing is incredibly lazy and bland too.