Seismic collapse is a critical failure mode in reinforced concrete moment-resisting frame (RC-MRF) buildings, particularly those with poor construction quality and low concrete compressive strength. To address this issue, this study investigates the impact of adding minimal shear walls to improve lateral stiffness and prevent collapse. A reference model was created, simulating four levels of concrete strength deficiency: very slight to severe. Numerical analyses were conducted on 3-, 6-, and 8-story RC-MRF buildings, both with and without shear walls, under nonlinear dynamic loading. Key parameters such as story drift, plastic hinge development, and robustness index were examined. Results show that reduced concrete strength significantly increases story drift—especially at the first story in models without shear walls—resulting in widespread plastic hinge formation and increased risk of collapse. In contrast, models with shear walls did not experience collapse and showed improved seismic resilience, even under severe strength deficiencies. The study also found that the 8-story case was more sensitive to reductions in concrete strength. These findings highlight the effectiveness of minimal shear wall incorporation as a practical solution to enhance the seismic performance and safety of RC-MRF buildings with deficient concrete strength.