> mutual fund managers who generally underperform their index for years operating a relatively high-fee fund (compared with ETFs)

There is a bit more nuance here. The fund manager oftentimes has an obligation to follow a given mandate, which may not seek to outperform a given index. For example, investors may want exposure to specific factors (value, growth, momentum, etc.) or asset class (municipal bonds, preferred stocks, etc.). Additionally, investors may seek funds with better risk adjusted returns as opposed to funds with greater absolute returns. In these cases, managers are compensated for delivering on their mandates. The ETF space has similar high fee products.