“We find that over fast Internet, the UDP+QUIC+HTTP/3 stack suffers a data rate reduction of up to 45.2% compared to the TCP+TLS+HTTP/2 counterpart.”
QUIC was sold as the game-changer for web performance. On fast links it loses up to 45.2% of throughput to plain old TCP, and the gap grows as bandwidth grows. The culprit is receiver-side overhead from excess packets and ACKs handled in user space. The protocol built for speed gets slower exactly where the pipes are fattest.