Employee #1 is taking on 80% of the risk of a founder for usually a sliver of the upside. I know a lot of single-digit startup employees and I really think you're doing them a disservice by characterizing that role as really at all less stressful than being a founder.
You see founders parachute straight into consulting or speaking after flaming out of their tech startup. Their team needs to go get jobs.
I can't speak for everywhere on earth but in this current Bay Area tech job market, I can just as easily parachute into a well-paying, full-time gig at $TRENDY_TECH_COMPANY. You build interesting experience & insight being the first-hire and, if you're actually a skilled engineer, shouldn't have a problem finding your next job in about 4 to 6 weeks if things don't work out.
It's still stressful but nowhere near as stressful. For instance - employees get a salary, founders usually don't. That alone makes a huge difference. The founder has to keep the startup alive, try to find funding, direct the product all while one bad decision could kill it. The employee has to do what the founder asks, do it well, and go home at the end of the day. Being an early employee is still more stressful than a normal job especially as there is no one to help out if you're stuck, but I think the difference between founder and early employee stress is vast.
You see founders parachute straight into consulting or speaking after flaming out of their tech startup. Their team needs to go get jobs.