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Exciton-polaritons, strongly-coupled light-matter quasiparticles, can preserve the valley selectivity of monolayer transition metal dichalcogenides embedded in a microcavity. The cavity field character of the exciton-polaritons modifies the emission properties of the monolayer, leading to preservation of luminescence polarization at room temperature distinct from bare monolayers. Here, we explore both experimentally and theoretically broad regimes of cavity coupling with MoS₂ and their impact on exciton-polariton valley polarization observed over a large temperature range. An intuitive and general cavity coupling model captures these observations by considering the relative rates of exciton and photon relaxation and intervalley scattering. The experimental and theoretical agreement demonstrates that exciton-polariton valley polarization dynamics can be well-controlled using cavity decay rates, coupling strengths, and detunings by microcavity engineering.