^^^^Whatever would those two ideologies now trapping humanity be?
As to the main topic, remember the most brilliant victory is the one won without fighting. Any notion that a satisfactory climax involves the humans actually defeating the Vorlons and the Shadows is childish. A major point of the series is that the Shadows and the Vorlons keep playing war games because they aren't paying any price for it. If either the Shadows or the Vorlons attempted to continue their attack on the supporters of the other, then they would be facing the combined might of the enemy (alone more or less equal,) the united lesser races, and the remnant First Ones brought by Ivanova. That coalition would exact altogether too high a price for their glorified hobby. The only way Shadows and Vorlons could continue is to make an agreement---then the lesser races, even with the First Ones, wouldn't have a chance. But then, if the Shadows and Vorlons could have agreed, would there have been a cycle of wars in the first place?
The climax is better than thrilling---it's honest and inevitable.