Back in the day, when those new fangled relationship database things came on the scene, do you think people would have been well advised to try and find work on the actual database engine itself, instead of the more frivolous work of using the new technology to, say, solve actual business problems?
If you are not rigorous, then what you are doing is essentially "black art". It may work for some tasks ad-hoc, but with the rapid pace of model improvement your skill will likely become irrelevant/not needed quickly.
You need some amount of experimentation to get the best results but in my experience what works for one model does nothing or worsens the output in others. Adding loras and different types of images into the equation makes this so variable that I would never consider it useful besides keeping a few key words I used to get x good result on y model and experimenting with those when I start a new project.
Calling it "prompt engineering" seems odd.
I don’t think LLM offer standardized API like that ?