A/B testing is an effective approach to use science to design and deliver deeply-frustrating user experiences.
A/B testing without upfront research is just random monkeys testing random designs to see which of those designs do “best” against random criteria.
If drug testing was actually implemented like most A/B tests, you’d give 2 drugs to 2 groups of people and pick the “winner” by whichever group had fewer deaths.
I want you to consider instead the possibility that Waterfall came to exist, and continues to exist, for the convenience of managers: people whose methods are inherited from military and civil engineering, and who, more than anything else, need you to promise them something specific, and then deliver exactly what you promised them, when you promised you’d deliver it. There exists many a corner office whose occupant, if forced to choose, will take an absence of surprises over a substantive outcome.
Features don’t work, in the sense that they can be easily gamed. A brittle and perfunctory implementation, done quickly, is going to score more intramural brownie points over a robust and complete one. If the question is "does product A have feature X?" then the answer is yes either way.
We use the term feature factory as a pejorative to designate companies addicted to adding features, while accumulating incalculable so-called technical debt. This situation is driven by management for the convenience of marketing, and I am skeptical that a more faithful application of Agile principles will correct it. Indeed, I suspect Agile processes are constitutionally vulnerable to this kind of compromise.
The presence of a feature can only indicate to a user if a goal is possible, behavior will determine how painful it will be to achieve it.