The reason that you must include the full component XML when creating a baseline is because that is what happens in the console when you create a baseline. Baselines contain copies of all of the sources of the components that they contain so that if the source is modified it does not modify the baseline behavior. Baseline components contain pointers back to their sources so that when the sources are updated the baseline can let you know that it has an old copy and it should be resynced to have the updated copy if desired, BUT it is not actually necessary that source of the component be available and the baseline will still function.
This should mean that in some cases I could export a baseline from my infrastructure, send it to you, and you could import it and use it even if you never had access to any of the sources and they never existed on your end… the baseline should still function.