No one disputes that sometimes imperative styles of programming are clearer, or more efficient. Efficient functional programming is a new topic that is growing in importance as it becomes clear that the future is rooted in highly parallel programming.
But these specific complaints mounted at Erlang don't really ring true to me. For one, it's idiomatic to pass state along in functions, and it's not difficult at all to write branching logic based on a variety of cases in state. Now, if you have hundreds of fields in your state you will surely find Erlang to be more awkward than other functional languages, because you can't do things like pattern match and run guards into dictionary structures. But this isn't a failure of "functional programming", it's probably more of the nature of Erlang. Erlang just isn't optimal for that kind of work.
It seems to me like the author's complaint is more "Erlang wasn't the best for my projects and programming style" rather than "Functional programming has failed." Erlang is written by engineers who understood their target domain very well and wrote a very elegant system for wrangling it. Game development wasn't exactly on that list of things Erlang was meant to do well. :)