Series begins from the POV of Farm Boy Protagonist™ during some sort of "harvest festival" type scene, and after the festivities a mysterious stranger pulls him aside and offers to pass down a sword that will make him an archetypical master swordsman but he has to hunt evil mages. There are several other archetypical heroes with similarly inherited powers, all for the purpose of stopping evil mages.
There's not a lot to go on here, but to me it feels like it might be Lawrence Watt-Evans' The Annals of the Chosen (2006-2008). The first book The Wizard Lord does have a young man, Breaker, passed the mantle of the Swordsman, one of the Chosen who are tasked with destroying the Wizard Lord if he turns evil (at which point he becomes a Dark Lord). (The previous Swordsman wants to retire, so the mantle is handed off peacefully.)
Breaker finds himself wondering about things that are happening, so he goes in search of the other Chosen to consult with them. As more of the Chosen gather it becomes more obvious that something has gone wrong with the Wizard Lord and they end up having to destroy him.
The second book The Ninth Talisman starts differently, potentially adds a new member to the Chosen, (which happens every time a Dark Lord is defeated) but still ends up in a power struggle between the Wizard Lord (who hasn't quite gone Dark) and the Chosen. This time the conflict carries through into the third book The Summer Palace.