What would the other advantages of A|B testing be for a corporation instead of widening the funnel, increasting lifetime revenue or other such bottom-line focused goals?
The downside with hired testers is that they are unlikely to be a statistically representative sample of your target market. I don’t think this is actually a problem for most startups or new products being launched by major players, since a lot of UX issues early in product development will be obvious to anyone who isn’t the original developers, and the number of actual users you have won’t be big enough to serve as a statistically representative sample of your target market anyway.
explaining what your product does is hard when you’re the product expert. A/b testing ad copy helps folks parse what your product does.
If your product is actually good then having more people understand what it is, is also good.