I work with the author regularly, and am inclined to a more charitable reading. I was serious when I suggested that he'd love to receive your Rust benchmark showing that it has no slowdown, and would happily include a note about them.
I'm not sure of the the purpose of the "obfuscation" comments. I'd guess that they were intended as jokes, but missed the target. Rather than mocking the use of reduce, I think his goal was probably to defend the utility of the humble for loop. On a larger level, both he and I have a concern that people often assume "a sufficiently clever compiler" without checking to see that they actually have one.
Here's the sort of thing I've been working on him with: https://arxiv.org/abs/1611.07612. It's shows how to count number of set bits with SIMD in a way that is faster than the using the builtin POPCNT instruction. This is a different level of optimization than concerns most programmers, but if you are trying to get that last 50% of maximum performance out of an implementation, it's likely that (at this point) Swift shouldn't be your top choice.