Most software projects don't even do A/B tests. A lot of them don't need, it's just what someone wants to ship. Another set can't even get to the sample size required.
But fine, let's take the subset of features / projects that can be tested or somehow validated. In my experience (having worked for 13+ years on companies that prefer to A/B almost everything), more than half of the tests fail. People initially might think the solution is to have better ideas, cook them more, do better analysis. That's usually wrong. I've seen PHDs with 20+ years of experience in a given industry (Search) launch experiments and they still fail.
The solution is to have some sort of "just enough" analysis like user studies, intuition, and business needs, and launch as fast and as many as you can. Therefore, development speed is A bottleneck (there's no Silver Bullet so it's not THE bottleneck).