First, it wasn't just another cliched shootout. Second, it was following a theme JMS had from the start. That despite the power and knowledge posessed by the Vorlons and the Shadows, they weren't gods, they didn't know and see all. And like humans, and reasonably, any sentient being, when taken from their comfort zone, they become insecure.
That's all acceptable to me. I had no particular desire to see the war end in a shootout. What was unsatisfying was the unbelievably weak way it was executed and, in addition, the very jarring effect of having spent over three seasons on this and then have the Vorlons and Shadows and the war disappear in an instant. Of course, maybe something in the future explains this and I'm just not there yet. I'm open to better undetstanding things as I continue to watch.