Comment by Veserv

That is because providing a reliable stream over a stateful connection is actually about a half-dozen layers of abstraction.

TCP couples them all in a large monolithic, tangled mess. QUIC, despite being a little more complex, has the layers much less coupled even though it is still a monolithic blob.

A better network protocol design would be actually fully decoupling the layers then building something like QUIC as a composition of those layers. This is high performance and lets you flexibly handle basically the entire gamut of network protocols currently in use.