What “would be” converters don’t understand is that there are large and quite complex torque waves traveling up and down the crankshaft. These either get reflected, transmitted or damped at the ends. The engine designers take this into consideration but if converters mess with the dynamics then you can get weird and wonderful effects.
Examples: rotax explaining what will happen if the engine is run without a propeller, the Jabiru flywheel attachment saga, various prohibitions on rpm ranges and so on. Even the big radials had issues:
https://www.scribd.com/document/3256...800-Crankshaft