I think many/most people who talk about working extreme long hours are posturing. They want to seem hardcore for the sake of career advancement, investors, etc.
What they really mean by 100 hours per week or whatever is that they respond to emails or chat on slack at all hours.
And while that's "working" in a way, it doesn't mean doing deep focused work for anything close to that number of hours. It just means they're on call, or else that work is their social life and they spend their free time chatting/hanging out with coworkers.
You can see this on social media with people who claim to work 100 hours and yet they clearly spend hours per day on twitter/instagram, go to the gym every day, go to parties, go on dates, travel, etc. The numbers obviously don't add up. I'd bet a lot of these people actually work less than the typical 9 to 5 engineer. It's more about being part of a sub-culture than anything else.
People who have actually worked crazy hours doing focused work like engineering for periods of time know that it's not sustainable long term. Your body and mind start failing you in various ways. Creativity and problem solving take a nose dive. You can do it for awhile but it becomes counter-productive before long.