If they are so concerned with low latency, how come they are wasting an entire roundtrip (the "OPEN + OPEN/ACK") before sending any data? I mean in TCP it's no

If they are so concerned with low latency, how come they are wasting an entire roundtrip (the "OPEN + OPEN/ACK") before sending any data? I mean in TCP it's not allowed (Even though, super-theoretically, it's not completely forbidden) to carry a payload in the initial TCP SYN. If you're so latency-obsessed to create your own protocol, that's the first thing I'd address.