LLMs are a higher level construct than PID loops. With things like autopilot I can give the controller a command like 'Go from A to B', and chain constructs like this to accomplish a task.
With an LLM I can give the drone/LLM system complex command that I'd never be able to encode to a controller alone. "Fly a grid over my neighborhood, document the location of and take pictures of every flower garden".
And if an LLM is just a 'text generator' then it's a pretty damned spectacular one as it can take free formed input and turn it into a set of useful commands.