Internet is crawling (single-digit Mbps or less) and the user blames "the Wi-Fi", but the Wi-Fi link is measurably healthy: strong RSSI, high negotiated PHY rate, and a 2-3ms ping to the default gateway with zero loss. No local process is consuming bandwidth. Standard Wi-Fi troubleshooting (channel changes, band switching, moving closer to the AP) is wasted effort because the bottleneck is entirely on the WAN side. The failure looks like a LAN problem to the user because that is the only part of the path they can see.