The service life of hot-rolling descaling rollers is severely limited by premature failure under synergistic high-temperature friction, wear, and alternating loads. Herein, non-spherical WC particles replaced conventional spherical WC to fabricate Ni-based composite coatings via plasma arc surfacing, so as to reveal the regulation mechanism of WC dosage on multicarbide evolution and high-temperature failure mechanisms. With WC contents of 30-65 wt.%, the microstructure transformed from sparse carbide dispersion to uniform multiphase refinement and ultimately to brittle coarse carbide networks. The results confirm that WC content below 45 wt.% optimizes carbide distribution and refines microstructure. The optimized coating acquires a refined grain size of 27.1 μm, high microhardness of 827 ± 3 HV1.0, and a low wear rate of (3.719 ± 0.4) × 10−6 mm3/N m at 400 °C, maintaining excellent strength–ductility balance and better high-temperature performance than high-WC counterparts. Fine-grain strengthening, dense oxide films, and strong interfacial bonding jointly inhibit oxidative–adhesive wear and crack propagation. This study clarifies the linkage of non-spherical WC content, multicarbide evolution, and high-temperature performance, guiding high-performance wear-resistant coatings for hot-rolling components.