Performance assessment of control systems has been receiving growing attention in the recent past to improve operability and profit margins of the process. However, such studies, and also the tools available to carry out such studies, from the plantwide perspective are rather limited. In this regard, a new dynamic performance index, called dynamic disturbance sensitivity (DDS) is proposed in this paper. It is then used to assess the performance of three plantwide control (PWC) structures (CS1, CS2, and CS3) for an industrially important petrochemical process, namely, the hydrodealkylation (HDA) of toluene to produce benzene. The three control structures are distinctly different from the throughput manipulator standpoint: CS1 uses an internal manipulator (e.g., reactor temperature), CS2 uses a fixed-feed control strategy, and CS3 uses an on-demand control strategy to control throughput; consequently, the rest of the control structure decisions are significantly different. By analyzing the results from rigorous nonlinear dynamic simulations, CS3 is observed to be exhibiting the poorest overall dynamic performance. The plantwide dynamic performance of CS2 is found to be superior or comparable to that of CS1 for all the anticipated disturbances. The analysis of the results reveals the effectiveness of DDS and rigorous simulation tools for PWC studies.