Surely this is way too broad a statement?

There are small A/B tests which absolutely make sense. You often see marketing sites making small tweaks to banners and copy. It's not that one has worse UX or even that one is objectively worse, just that different users have different preferences and it's often difficult to know exactly what will work best.

Similarly you can be very confident of something, but A/B testing it still reduces risk. Any significant change should probably always be rolled out to a small fraction of the user base first in case you accidentally change something for the worse.

I agree if you're talking about some BS experiment where a company uses A/B testing as an alternative to putting the hours into product design and user research.