Jumbo was the famous elephant that PT Barnum exhibited. His name came to stand for the big story, for the audacious claim, for making quite a noise.
You probably need more Jumbo in the story you're trying to tell.
Mumbo, on the other hand, is deliberately obfuscating the facts. Mumbo is manipulation, the creation of placebos that don't scale or the extension of power without the facts to back you up.
No more mumbo please.
Feel free to quote me on that the next time someone brings you a big heaping plate of hype.
[In fact, Mumbo-jumbo was probably a term that was xenophobic when it was first used more than a century ago (having nothing to do with elephants but probably something to do with an exotic religion), but I think it has evolved to have more to do with technology and slick salesmanship now.]
Mumbo just doesn't last as long as it used to.