I'd say you'll probably spend more money on medical bills I'd you were to work 18 hour days 5 days a week for any meaningful amount of time. Or one might be sorely mistaken about what constitutes 18 hour work days - does that include travel and eating time too?
That schedule seems untenable even in the fairly short run. If you really need to work 90-hour weeks, six days of fifteen hours (and just one day off in stead of two) feels much more like something you could keep up for at least a month, perhaps even more.
If nothing else, 18-hour workdays leave at the most five hours for sleep (and only one for everything else, like mealtimes and hygiene), so you'll be pretty damn bushed come Thursday and Friday. 15 hours of work would leave seven for sleep, and double your everything-else time to a luxurious two.
Are you trying to say "it's easy to be financially successful by working 8 hours a day instead of 18 hours"?
like... it's "overstated" that people think they need to "work more/work harder" to become successful?