why do weak people keep thinking that they can beat someone so strong they beat the demon king that the whole world feared? like seriously no army was capable of even coming close to the might of the demon king combined yet they think ganging up on the person who beat said demon king is gonna go any better.
They weren't there. They never faced the demon king personally. Viola is the only one of the bunch who did, and she's not underestimating Blum. Those knights seem arrogant enough to believe that they could have taken Blum's place in killing the demon king, if given a chance. However, they were elsewhere, if not still in training, when the demon war happened, so they simply weren't given that chance. It's not an unusual thought pattern. In RL you see it exceptionally often when random people look at something that had been done for the first time. Unless it was something totally crazy, they will remark that they could have done it as well, if they just had thought about it first, so it's nothing special.