I stand by my initial post - each branch of our government is, by definition, a check against the other branches.
I agree with your assessment of the legislature - they wouldn't last at UPS, where results matter.
But it's not enough for the executive to say, 'It's important, believe us'.
That's not how things work, and in this case, Trump and his team simply didn't have a case.
Now, if they changed the EO, we might be having a different conversation.
But, like so many things about this nascent Presidency, they seem to like to shoot first, and aiming seems to only happen when they're questioned.