Think of it more as it is reasonable to say there is NOT a 100% chance that AI will save humanity, i.e. don't count on it. In the same way as it would be unwise to count on there being a 0% chance of AI killing us.
Whether or not the 90% (optimistic focus) or the 10% (pessimistic focus) numbers are accurate is less the point. But the shape of the distribution and how to navigate that is the bigger thing to think about.