The answer is that the ban, as written, as so egregious that it went beyond even those broad 1952 powers.

Had they exercised a little guile and tact, it would have stuck. The main issues seem to be 1) inclusion of people who already had permission to be in the US (green cards, valid VISA)  2) exclusion of  nations from whence real (as opposed to imagined) terrorists had actually originated 3) the inclusion of no non-Muslim nations.

Leaving out green card and valid VISA holders, including Saudi, UAE, and Indonesia and adding  a token non-Muslim country (maybe Albania) to the list would have pretty well assured that it would have stuck.

Thankfully (from my point of view), Bannon is not that smart.