The February 6, 2023, Kahramanmaraş earthquake doublet subjected reinforced concrete (RC) buildings in southern Türkiye to exceptionally severe near-fault seismic demand, with recorded ground motions locally exceeding the highest design level of the current Turkish seismic code. This study investigates the seismic performance of RC buildings based on post-earthquake field observations conducted across eleven affected cities, with a particular focus on comparing damage mechanisms in older building stock and in more recently constructed code-era buildings. Field evidence indicates that damage in older RC buildings was predominantly associated with well-established deficiencies, including inadequate detailing, poor material quality, soft-storey mechanisms, torsional effects, and pounding between adjacent structures. In contrast, severe damage observed in newer buildings was more closely related to structural system inadequacy and implementation-related shortcomings, such as low shear-wall ratios, inconvenient wall distribution within the plan, and deficiencies arising from construction quality and site supervision. The findings demonstrate that, while successive improvements in seismic regulations have significantly enhanced design requirements, satisfactory earthquake performance cannot be ensured by code-compliant design alone under extreme near-fault shaking. Instead, structural performance is strongly influenced by system-level adequacy, execution quality, and site conditions. The study provides field-based evidence highlighting the need to strengthen not only seismic design provisions but also implementation practices, construction control, and site-sensitive decision-making to improve earthquake resilience in Türkiye.