Getting a bit pedantic, but a few corrections:

1. That origin is just urban legend. Americanos started in the 70's.

2. Per ounce, you're technically correct about the strength of espresso vs. drip/brewed coffee. But brews have variable strengths, and most Americans drink 12, 18, and 24 ounce drip coffees (which ends up being more caffeine than even a quad shot of espresso).