Are 2021 buyers who are now selling at a loss (giving up their 3-4% rate) actually losing money?

Selling below what you paid and losing money are two different calculations. Run the full picture before deciding which one happened. Start with equity. Someone who bought during a fast-appreciation stretch, in a market that has since given some of that back, might still be up a few percent on paper. The problem is the round-trip cost of transacting. Add agent compensation (negotiable post-settlement, but real) plus closing costs on the sale, plus whatever they paid to close as a buyer on the way in, and the total commonly runs several percent of the price. A small paper gain gets eaten by the cost of getting in and back out, and the best case is roughly breaking even. The deeper point is time horizon. Counting on a home to make money in a year or two is a bet on the kind of rapid appreciation that has been a rare anomaly historically. That's why we frame a purchase around a five-to-seven-year hold. Over that window, price wiggles and transaction costs get absorbed and the leverage works in your favor. Over eighteen months, they dominate. Nobody can promise where any given market heads next. The protection is owning long enough that a short-term dip never forces the sale.