Of course the safe shut down has many more aspects than the single blade. But the unbalance loads are important, because they drive the aircraft structure compliance. If the engine lose say 5 blades and has a safe shut down, it can be certified, but will remain the most expensive fan ever, because nodoby can install it and certify an airplane able to withstand the FBO loads.
With modern, wide chord fan blades, unbalance loads have increased. As pointed out above, in the 90s FAA and JAA became aware of the issue and drafted AC25-24. The airframer have to demonstrate safe 3-hour diversion with a windmilling engine, covering strcuture, system, structure and human factors. The recent USAF E-11 (Global Express) accident report shows that vibrations are such that flight crew can barely read instruments to the point of shutting down the 'good' engine...