A hundred soldiers ably led defeat a thousand without a head. Take out the leadership, or, as we parse it in 21st century warfare: disable the Command and Control hubs/nodes
But OoTS has a robust command structure: Haley as second in command has grown. Even though as a leader she's not as good as Roy, she's still got the brains and the leader role figured out well enough to do the old "next adventurer up" thing. Plus, she's a Rogue, and I think she'll have a few counters to whatever Serini is trying to accomplish. And she has wands.
That was my gut feel.
That too.
On the other hand, standard adventuring party tactics is "take out the enemy casters first" and Serini was a long time adventurer ... do leopards reallly change their spost? Miko disabled V right off the bat when she took on the Order.