You make a good point Weaver in how things would be if networking was been designed today as a fresh start with the knowledge we have now, you are likely right I think the packets would be much bigger.
Of course the challenges of upgrading network technology is explained well in the video, they couldnt make QUIC its own standalone protocol as it would take a decade for middle boxes to catch up and be compatible as was the case with tcp fast open. So a very clever idea for it to piggy back on UDP something thats established and should be allowed by middle boxes. Every now and then on communities I see firewall rules that get posted that aim to block invalid combination of packets, I expect QUIC would violate some of those rules. But those arent standard rules configured by default on any devices.