In this case, the code size is about the same if you run as-is (if you're doing DOM manipulation, performance is likely a real concern). I'd agree it would be premature optimization if we were talking about moving from a map to a full-blown loop or something, but it's hardly a huge change.
Another great example is chaining myarr.filter().filter().map().map() or some such that I sometimes see. Lodash shortcuts normal map with the assumption of arrays without holes and then uses their own iterators to avoid multiple copies. This results in a huge performance boost.
A final consideration here is transpiling. The above methods would actually increase the code size quite a bit trying to work around any edge cases and hit performance even more.
"Premature Optimization" is always a matter of opinion. Some people might consider implementing quicksort instead of bubble sort to be a premature optimization. Others might disagree with me and believe that you should always use loops instead of forEach or map. In any case, this is hardly the only case for using call/apply.