A/B testing can be useful at times but it's largely overrated because you're only discovering the best design out of the ones you test. That means there could be a far better design that you failed include in the experiment.
Just because one design converts more than the other doesn't mean it's the design with optimal UX. I've seen many tests where the designs included already had faulty UX. This is why it's better to have a trained UX designer on your team who can fix basic flaws and present the best version of various designs for testing.