In this study, we investigate coherent exciton dynamics in a thin GaAs film using three-beam four-wave mixing (FWM) techniques. The GaAs film exhibits spatially varying biaxial tensile strain, enabling us to study the influence of differing strain on the dephasing time of strain-split heavy- and light-hole excitons. Heterodyne FWM experiments reveal an essentially homogeneously broadened exciton polarization throughout the film. While the exciton dephasing rates show no discernible correlation with the local strain variations, excitation-induced dephasing becomes the dominant FWM generation process at long dephasing times. Under cross-linear excitation the FWM signal mainly originates from two-exciton correlations. Theoretical analysis using the 10-level optical Bloch equations substantiates these findings. The strain resilience of the picosecond-scale exciton dephasing time suggests GaAs films as a powerful platform for investigating coherent light-matter interactions and coupling in composite exciton-plasmon quantum systems.