[carletoxtrs]

I have read how some alleged that the Mahaparinibbana Sutta has bits and pieces coming from later development

Yes, that was my first impression too. Your points make sense. There is a possibility that the Mara concept is just a simile. But then again, why isn't the sutta as clear about it as you pointed it out here, rather than introducing a simile which eventually leads to speculation and misinterpretation. That brings me back to my initial doubts about later additions.