I'd argue a well designed AI assistant would be considerably better than a decision tree for that use case. Decision trees are slow because you normally need to wait through several options before getting to the one you're interested in. (Though sure, perhaps not if your call is literally for the most common thing.) But with an AI you could jump straight to what you're interested in.

"Hi, I'm the LargeBank AI Assistant. How can I help you?" "I'd like to know the balance of my checking account."

And then authenticate and get the balance as usual. Simpler and faster. Agreed that it becomes a problem if it's seen as a replacement for human agents though. In an ideal world it would actually free up the human agents for when they're actually needed. In reality it'll probably be some of each.