Since its founding nearly two decades ago, Zillow has revolutionized the way Americans buy, rent, sell — and fantasize — about housing in the US. But a settlement that breaks the grip of powerful real estate agents could trigger a range of problems for the platform already suffering from declining traffic in an increasingly competitive housing market. The company’s stock has dropped nearly 13% since Friday’s $418 million settlement between the National Association of Realtors and groups of home sellers which ended the standard 6% commission for Realtors. It’s a sign that investors fear the settlement could have seismic effects...