A rotor blade for a wind turbine may generally include a first blade component formed from a first fiber-reinforced composite including a first thermoplastic resin material and a second blade component configured to be coupled to the first blade component at a joint interface. The second blade component may be formed from a second fiber-reinforced composite including a second thermoplastic resin material. The second fiber-reinforced composite may include a low fiber region and a high fiber region, with the low fiber region having a fiber-weight fraction that is less than a fiber-weight fraction of the high fiber region. In addition, the first thermoplastic resin material of the first fiber-reinforced composite may be welded to the second thermoplastic resin material contained within the low fiber region of the second thermoplastic composite to form a welded joint at the joint interface between the first blade component and the second blade component.