I understand why some people seem to be upset, but that may be because of a communication issue. I don't think there's anything wrong with the translation, but maybe something here is worded poorly? Just because Matthias can't possibly win doesn't mean he couldn't stall the guy. If he has some kind of innate power or gimmick like immortality or super regeneration, it could be a hell of a lot of trouble to try and deal with him. The fact that he was sealed to start with, and not killed, would imply that killing him either isn't possible or is extraordinarily difficult.
As for this being axed soon, no. This is apparently following the LN's plot pretty closely, though apparently the manga adaptation has more humor in it. Which I feel is a good addition to the story, honestly.