I don't think you have to be particularly bright to be a manager——that's more a quality you need in a leader.
我们仔细品读一下这个句子的意思。句子意思是,我认为当经理无须特别聪明。特别聪明是你当领袖才需要的品质。这个句子中显然没有“你需要领袖的品质”这层意思。我认为作者这句话中,in = as。即that's more a quality you need as a leader. 所以,in a leader是定语从句中的状语,而不是that(即quality)的定语。所以我认为 you need in a leader 整体是一个定语从句,其中in介词短语是定语从句的状语。