Faster here has many different meanings. The tests in that benchmark are more batch processing tasks. But that is not the only measure of speed. Zen I believe is more tuned for desktop use and keeping the system in a more snappy state which comes at the cost of some raw throughout performance. There is forever a tradeoff between latency and throughput, optimising for one is generally done at the expense of the other and both are optimising for performance, just different kinds.
I only mentioned zen as one of the official alternative kernels that is worth a look at though, making no claims as to if it the best for anyones particular workloads.
This is why it is best to do your own benchmarks for the stuff you care about and pick the best solution for your situation.