calculating IRR which as you know is a much more comprehensive measure than simply ROI. However, since you brought up ROI, what would you calculate the return on your investment if you didn't invest anything, but receive returns in perpetuity regardless of how small those returns are. For all intents and purposes, they are infinite. I didn't say anyone would become a multimillionaire off of a penny investment because it returns an infinite percentage.
IRR is a true formula and widely accepted so I am confused as to what you are referring to here, "they've stumbled upon some special "formula" (your word)"

This is a real world example and so since my math is fuzzy calculate my return for me.
I purchased a property at 1/4 its value. Because it was purchased so far below value, I obtained a loan for greater than the purchase price that i used to rehabilitate the property which I then rented out before the month was up. The mortgage, taxes, and insurance as well as management fees are 25% of the gross rent. The check we receive every month after all expenses is double the mortgage. What would you calculate our return on our non-existent investment to be?