> This is a case where this speed optimization actually wastes time overall.

That's too much of an absolute to be a good rule. If your heavyweight runtime is being launched 1000s of times to get a job done but you only do this once every few months, sure, don't do many optimizations, certainly don't worry about a rewrite in another language. The savings probably aren't worth it. If your heavyweight runtime is being launched 1000s of times to get a job done every day or multiple times a day, consider optimizing. Which may include changing the language. That's hardly controversial, this is the same thing we consider with every other programming task.

Is X expensive in your language and do you have to do this frequently? Then minimize X or rewrite in a language that handles it better.