I'm actually not so sure about that statement. For example, knowing if the code will be executed on a raspberry pi, a HPC with 10TB RAM and 512 CPUs, or a home desktop with 128GB RAM and 8 core CPU will greatly affect how the task may be done. Also, if code aesthetics are important with dependencies that allow it, or fewer dependencies are required, or if performance is more important, or if saving disk space is paramount, etc.
All of these considerations (or if the need to run on any of them easily) heavily change the direction of what should be written, even after the language and such have been chosen.
So, yeah - effectively you do need to specify quite a bit to a senior dev, if you want specific properties in the output - so it's obvious that this needs to be specified to a linguistic interface to coding like these LLMs.
I guess it depends on how you'd define "senior" in this context, someone who knows lots of techstack or someone who has an idea. Of course that doesn't directly map to people's skills because most people develop skills in various dimensions at once.