We present 3D simulations of semirelativistic collisionless magnetic reconnection, where upstream ions are subrelativistic while electrons are ultrarelativistic. We employ the realistic proton-to-electron mass ratio and explore a range of upstream ion magnetizations spanning 2 orders of magnitude, with our highest-magnetization run achieving unprecedentedly large domain sizes. Through a parameter scan, we find that as the system transitions from mildly to trans- and ultrarelativistic regimes, the qualitative behavior of reconnection becomes strongly influenced by 3D effects mediated by drift-kink and flux-rope kink dynamics. As a result, magnetic-energy dissipation at high magnetizations, and the subsequent nonthermal particle acceleration, can become less efficient, contrary to general expectations for 3D relativistic reconnection. Our results have important implications for understanding reconnection in magnetized astrophysical scenarios, such as the surroundings of black holes and neutron stars.