The main drawback of Struts 1.x is having only a single controller servlet (ActionServlet), which creates a potential bottleneck since all requests must pass through one point. This can limit scalability and makes it harder to modularize large applications. Options A, B, and D (backword overflow, forward overflow, no forward overflow) are nonsense terms not related to Struts architecture. Struts 2 and later frameworks addressed this by allowing multiple controllers.