I just think he DOES have eye for talent.. it is just that he is so angry that he sort of got blinded. i do wonder what he is so angry about. it is definetly not them he is angry at. he only lashed out at them is all.
so good he can atone for it by working for them for free.
The dagger is probably some kind of suicidal weapon and add to that it being wielded by a slave. Can easily understand his rage, if this turns out to be the case.
Maybe it's not the first time this has happened or maybe his services were used by a lot, even good people, but it still led to all their early graves, as they wielded weapons too powerful for them. Old grumps prolly expected the mc to go "crank this from 11 to 22".