(funny enough I tend to use for(let i = 0; i < arr.length; i++) loops most of the time anyway because the iterator protocol adds too much overhead for my tastes, so I wasn't likely to ever bump into this in the first place)
… but in a way you're correct that this is rarely the actual bottleneck in the surrounding code. Still, "death by a thousand papercuts" and all that. Plus having old-school for-loops as a habit makes it easier to spot the true botllenecks.
Also, for the record: I presume you tested on Chrome, but on Firefox the difference between the two loop styles is quite a bit larger (and generally slower than Chrome, so perhaps also a consideration when optimizing for "slowest browser" as the bottleneck).