Now, what he's talking about is at least parially true.... the market is very concetrated. And index investing does screw with "price discovery" much to the shagrin of the professional financial advisors. They HATE that people can consistently outperform active fund managers by just going "VOO and chill." And of course, he wants to sell you his ideas on how to "protect yourself."

But here's the thing. He already told you how to stay out of trouble: DON'T PANIC. When the market corrects, and it will sooner or later, do not panic sell. Stay the course. The market WILL recover. It always has. It always will.

If you depend on your portfolio to live, make sure you at least a year's worth of expenses in a liquid, stable form (cash or equivalent).