It is a nightmare for me, and I do somewhat regret taking the contract even with the sizable hourly rate.
In my eyes, programming makes sense. Even if I introduce bugs, I can sooner or later track down the issue, facepalm, resolve it, and move on with my day, with some semblance of accomplishment and lessons learned.
My prompt engineering work offers no such rewards, and is a total time-suck. This is because, as another commenter wrote here, it is "throwing shit at the wall and hoping it sticks."
While you can treat it as a scientific endeavor, testing hypotheses against a black box, you will never find a prompt that works consistently, even with a low temperature, solely because these models were not built to give consistent results. There is no end-all solution, there is no "correct prompt."
Companies employing prompt engineers are looking for such consistency. Prompt engineers are therefore stuck in a system where they simply cannot succeed. They can hope and pray that the testing done by managers produces fruitful results upon every test, but the results are, for all intents and purposes, random.