I am baffled you can even get to six figure LoC implementing QUIC. Having done the majority of a QUIC implementation before deciding I needed to design a new protocol that fixes QUIC's performance limitations, a minimal, but fully functional and performant implementation with zero dependencys (except for cryptography) should only take maybe 5,000 lines.

If you use the default parameters with such a implementation you will likely cap out at a pretty slow ~10 Gbps/core, but if you reduce the ACK frequency you can probably get to ~30-50 Gbps/core without too much trouble.