There's something to be said for both strategies. Once you get down to a functional and complete design, it's useful to A/B test details to optimize. But it's

There's something to be said for both strategies. Once you get down to a functional and complete design, it's useful to A/B test details to optimize. But it's nearly impossible to design something using an A/B test. Design simply does not work that way—it is not an evolutionary process on three variables, initially whether you believe in it or not, it is an art and as such takes in thousands of variables in thousands of forms and outputs something that works. That's the job of the expert—at the beginning, they are using their internal A/B test to produce something they know will be successful in the grand scheme. Give them a chance, please.