Yes, absolutely. They demand a lot of hard work, much more than your typical public university. As you go through life however, you start to realize that accomplishment comes from working hard on the right things - a subtle but important distinction from plain old hard work.
Imagine that you are running and come to a wall. You are big, strong, and have lots of resources at your disposal. You almost certainly can bust through the wall and keep going. Do you do it? Or do you check to see if there is an unlocked door around the corner? The reward for you is exactly the same (a grade of A in the class; a promotion at work) and you aren't the person that has to clean up the mess you leave behind. What do you do?
The Ivy League schools have plenty of people that would choose one option and plenty that would choose the other. The other schools don't have very many people for which busting through the wall is even an option, which is definitely not the same thing as "working harder"
Potentially unpopular opinion: This is why I’m actually very bullish on graduates from famously demanding colleges like Ivy League and other competitive universities. To graduate, you can’t just be smarter than average and coast your way through to graduation. You actually have to work hard and be able to self-motivate to do hard things even when it’s not intrinsically interesting.
That doesn’t mean that graduates from average colleges can’t work hard, of course. It’s just much harder to tell if someone has learned to work hard or if they just coasted through life up until this point if you can’t look at their resume and see any particularly difficult achievements.