This work provides a comprehensive photo-OER kinetics investigation on crystalline TiO₂ surfaces through a reaction-diffusion kinetic model. Our findings show that while the OER necessitates the accumulation of multiple oxidizing equivalents, the process does not exhibit a higher-order rate dependence on hole concentration, as the holes arrive sequentially. This nuanced understanding challenges the conventional interpretation of rate laws. It highlights the critical need for caution when extrapolating apparent rate laws to the microscopic processes that govern complex reactions such as OER, especially those involving coupled reaction-diffusion phenomena. Under low light intensity, hole formation and diffusion within the bulk crystal predominantly drive the reaction. However, as light intensity increases, the reaction becomes nearly independent of light intensity due to the buildup of intermediates requiring thermal activation to proceed. This shift in reaction kinetics underscores the importance of thermal steps, which have often been overlooked in studies focusing solely on photogenerated carriers. A controlling influence of thermal processes on a photo-driven reaction has also been identified in a computational study of a very different system, the dye-catalyst diad for water oxidation and may be more common than currently appreciated. The localized accumulation of immobilized holes has a higher OER rate than holes that are free to diffuse, making them the principal contributors to surface reactions in situations where hole mobility is restricted. This suggests the necessity of considering hole immobilization in any realistic model of catalytic processes on TiO₂.