Epitaxial growth of graphene on silicon carbide (SiC) offers a promising route to high-quality and wafer-scale graphene directly on a wide bandgap semiconductor, eliminating transfer-induced contamination. Conventional growth, however, relies on extremely high temperatures that often provoke severe step bunching on the SiC surface, impairing graphene uniformity and device performance. To overcome this limitation, we present a stepwise growth strategy that exploits buffer-mediated kinetic control, with first-principles calculations confirming its thermodynamic feasibility. The process employs a carefully controlled two-stage temperature program. First, a continuous buffer layer is formed on SiC(0001) at a relatively low temperature. This layer acts as a diffusion barrier, confining sublimated Si atoms to step edges and suppressing terrace-scale atomic migration, thereby inhibiting giant step bunching and stabilizing the surface morphology. In the second stage, raising the temperature drives graphene growth. The pre-formed buffer layer serves as a carbon reservoir, delivering a uniform supply of precursors across terraces and enabling dual-site nucleation at both steps and terraces. This promotes rapid lateral expansion of monolayer graphene while further suppressing step bunching. Compared with conventional high-temperature direct growth, this stepwise approach substantially reduces giant step bunching, disrupts the step-edge-dominated nucleation paradigm, and yields more controllable nucleation alongside a stabilized surface morphology. As a result, large-area, uniform, and high-quality monolayer single-crystal graphene can be reliably obtained.