Climate change has intensified extreme heat events in China’s megacities, posing severe risks to public health. Parks, as key blue–green infrastructures, can alleviate urban heat, yet most assessments rely only on land surface temperature (LST), overlooking thermal comfort. Taking Shanghai as a case, this study introduces the Modified Temperature–Humidity Index (MTHI) and integrates park vector data with mobile phone signaling populations to evaluate cooling benefits from both temperature and comfort perspectives, with attention to urban–suburban differences. Results show: (1) suburban parks achieve broader LST cooling ranges, but high humidity reduces MTHI effectiveness; (2) park area, vegetation, and water coverage are positively correlated with cooling intensity, while vegetation coverage shows opposite correlations with cooling distance based on LST (positive) and MTHI (negative); (3) due to higher densities, core urban parks serve far more equivalent cooling populations than suburban parks, yet MTHI estimates are 54.5% lower than LST, indicating LST-based evaluations may overestimate benefits. The findings highlight the importance of incorporating thermal comfort metrics into park benefit assessments and suggest differentiated strategies: increasing small-scale parks in dense urban centers and optimizing suburban park design to enhance environmental thermal comfort.