TCP has major issues in low-latency environments. It has too many timers and they are too coarse for 50us RTTs and 100gbps bandwidth. QUIC as a transport for gRPC can solve a lot of this. What we know for sure today is that Linux distributions, out of the box, are garbage for TCP in datacenters. You can tune some of it away, if you happen to know where the knobs are, but some things like microsecond packet time stamps you have to patch. Switching to a UDP transport means you don’t have to argue with Linux kernel maintainers in order to make progress.