Slower overall very much depends on your workload and the way the code is written. However lambda is supposed to be short lived processes and AWS manage the concurrency so the actual performance difference of each language is mitigated somewhat for the average customer (edge cases will always exist).
It's also worth noting that if you're running the kind of processes that this does become a concern, then lambda is probably the wrong choice anyway. However, as always, the smart thing to do is build then benchmark (as the author did).
It's also worth noting that if you're running the kind of processes that this does become a concern, then lambda is probably the wrong choice anyway. However, as always, the smart thing to do is build then benchmark (as the author did).