A/B testing misses the point of statistical design of experiments, which is that your variables can interact. One factor at a time experiments are pretty much guaranteed to stick you in a local maximum
I do believe "doing A/B testing" is probably better than "not doing A/B testing", more often than not, but I think non-statisticians are usually way too comfortable with their knowledge (or lack thereof). And I have very little faith in the vast majority of A/B experiments run by people who don't know much about stats.
