Urban vegetation is widely promoted as a nature-based solution for mitigating outdoor thermal stress in hot-arid cities, but aggregated or static indicators obscure species-specific behavior, diurnal variability, and the linkage between outdoor comfort and building energy demand in courtyard environments. This study addresses these constraints by integrating outdoor thermal comfort mitigation and cooling energy performance using a reference-based, species-sensitive analytical methodology. The Vegetation Cooling Efficiency Index (VCEI) quantifies vegetation-induced reductions in Physiologically Equivalent Temperature (PET) relative to a non-vegetated reference scenario and is normalized by vegetation coverage. The PET-Energy Sensitivity Index (PESI) characterizes building cooling energy demand's responsiveness to outdoor thermal comfort. A hybrid approach integrating calibrated field measurements, hourly microclimatic simulations, and dynamic building energy modeling is applied to a university courtyard in Aswan City, Egypt, reflecting extreme hot-arid conditions. The canopy features of Cassia leptophylla (CL), Cassia nodosa (CN), and Ficus nitida (FN) are assessed across varied vegetation coverage ratios. The results show that vegetation covering alone cannot predict thermal mitigation outcomes. PET reduction is influenced by species-specific canopy structure, with peak-hour reductions surpassing 40 degrees C in dense-canopy species and significantly lower Delta PET values across vegetation coverage levels. The nonlinear relationship between outdoor thermal mitigation and indoor cooling energy demand underscores the necessity for a comprehensive comfort-energy assessment. The proposed indices allow for comprehensive, reference-based vegetation strategy comparison and transferable performance measurements for climate-responsive courtyard and campus design in hot-arid environments.