There are plenty of both types of investor here, and my own FIRE income will be about 60% rental income to 40% index funds, but the effort and temperament required for each are drastically different.
Index funds are essentially fool-proof. It's easy to describe how to start investing in index funds to a new or otherwise unsophisticated investor: Buy funds representing the entire market with low expense ratios. Don't sell when the market takes a turn for the worse. Granted, actually overcoming human nature and holding through bear markets can be difficult for some people, but it's a simple and effective concept.
Real estate, on the other hand, requires a fair amount of research to identify good investments. Many people buy rentals without even learning to properly evaluate them, but that's neither here nor there. If you want to purchase real estate and have it cash flow reliably for an extended retirement, you need to understand the entire purchase process, learn to manage either tenants or a property manager, oversee repairs and rehabs when necessary, file evictions if a tenant stops paying, and keep an eye on how local trends and legislation affect your business. Don't get me wrong: I love real estate and it doesn't have to be a huge amount of work to own it, but it is *more* work when it comes to education, preparation, and running your business. Most of my RE work comes down to decision-making... but it took time to learn enough to make informed decisions on a variety of topics.
Either is a great choice, so long as people are honest with themselves about which path is best suited to their personality and goals.