1. Your peer might use TCP and not support QUIC

2. It hasn't even finished standarization

3. It can be up to 5x less efficient than using TCP+TLS (personal measurement). If you don't require TLS it can be even worse.

4. It doesn't even answer the question that the article asks: You still have lots of options on how to get packets for your Quic endpoint to the application. You can use regular socket APIs, you can do some trickery using parts of the kernel stack (using eBPF). Or you can even do even more kernel bypass and using AF_XDP to get data into the app.

It depends whether you control both ends. If you need to talk to TCP clients then you have to use TCP.