Rabi splitting is a defining signature of strong light-matter interaction, emerging when a two-level system is resonantly driven by an optical field, resulting in a spectral doublet separated by the Rabi energy. In solid-state systems, Rabi splitting occurs at exciton resonances, where it is shaped by many-body interactions intrinsic to the material. Here, we investigate the Rabi splitting dynamics in two paradigmatic two-dimensional semiconductors: a hBN-encapsulated MoSe₂ monolayer and a (Ga,In)As multiple quantum well structure. In MoSe₂, strong Coulomb interactions dominate over light-matter coupling, while in the quantum wells, both interactions are of comparable strength. While both systems exhibit clear Rabi splitting under resonant excitation, their behavior diverges under increased excitation strength. MoSe₂ displays sublinear Rabi splitting due to excitonic correlations, whereas (Ga,In)As quantum wells reveal additional spectral resonances and coherent optical gain, indicating a transition beyond the simple two-level regime. These contrasting behaviors are quantitatively captured by a unified microscopic many-body theory based on Heisenberg equations of motion and an exciton expansion. Our findings elucidate the impact of many-body interactions on coherent exciton dynamics and establish a framework for tailoring strong-field optical responses in two-dimensional materials.