From the conclusion: cases where it performs well and poorly— both in traditional desktop environments but also in mobile and proxy scenarios not previously tested

Example: its benefits diminish or entirely disappear compared to unproxied TCP in low loss/latency cases, and when there is 1% loss. In the case of high delay links, QUIC still outperforms TCP [...]. Thus, proxies can help TCP to recover many of the benefits of QUIC, but primarily in lossy scenarios, and when the proxy is equidistant from the client and server