> So not only is it normal that the president defers to agency heads on the interpretation of the applicable law that they are experts in, it is the only way the system can function.

[Emphasis mine.]

Yes, well said. This is the ultimate bottom line argument!

The Constitution might as well not exist if individual actors with expertise the President does not have, are not expected to put their specialized understanding of previous orders, laws and precedent (and reality!!!) ahead of who they report to.