The video states A/B testing doesn't help you find the global maximum, which I agree with.
So how do you go about finding the global maximum? Using A/B testing you could create some variations that are 'wild' to hope to get lucky but it is not very efficient. What else can you do?
Having just used GWO for a project because it was a requirement (GWO is integrated with Shopify), I can now much more enthusiastically endorse Visual Website Optimizer.