Holmes' grift was grandiose though than just ripping off dozens of grannies. She ripped off some of the wealthiest and most informed people on the planet with a promise she couldn't keep, a complete lie. Her invention was never going to work no matter how she tried. Like, she is a nighmarish example of how toxic 'fake it till you make it" can be.

The character of Grayson in ICAL is smalltime hustler with big eyes but she's just a hustler. Holmes is a cult leader, which I suppose is a species of grifter.