I know this is a salty take, but reliance on A/B testing to design products is indicative of product deciders who don't know what they are doing and don't know what their product should be. It's like a chef saying, I want to make a pancake, but trying 50 different combinations of ingredients until one of them ends up being a pancake. If you have to test whether a product works / is good / is profitable, then you didn't know what you were doing in the first place.

Using A/B tests to safely deploy and test bug fixes and change requests? Totally different story.

A big tech company has ~10k experiments running at once. Some engineers will be kicking off a few experiments every day. Some will be minor things like font sizes or wording of buttons, whilst others will be entirely new features or changes in rules.

Focus groups have their place, but cannot collect nearly the same scale of information.