Dorei kara no Kitai to Hyōka no Sei de Sakushu Dekinai nodaga

A reincarnated boy, Allen, gets bequeathed by a goddess the cheat skill, "Restoration." Even though he can heal all and any injuries and illnesses, there aren't a lot of places where he can use that skill to the fullest, so he planned to "regenerate" the slaves he bought and lead a slow-paced life. But the healed slaves' cheats turned out so out of the ordinary that the crops they tend to and their living conditions turned for the better in a blink of an eye. The protagonist, Allen, who slowly but surely is robbed of opportunities to shine, tried to counter that with his modern knowledge, and yet, those talented slaves absorbed it all and brought success to any and all businesses. The protagonist is becoming irrelevant with each passing day?!