Based on the attached survey of practices, I propose a minimal edit to the help display.  Instead of "optional arguments:", we say "the options are as follows:".

The use of the word "option" is dominant is in the CLI world, followed by "action" and "switch".  The noun form "option" doesn't seem to cause the same confusion that arises in the adjective form "optional arguments" which strongly implies "not required".

For the documentation, I suggest adding a sentence or two in the introduction to explain the terminology used throughout the rest of the argparse docs.