Have you got any data to backup that claim?

It’s also a specious argument anyway. The six connection limit isn’t purely artificial, opening and tracking TCP connection state is expensive, and happens entirely in the kernel. There’s a very real cap on how many TCP connections a machine can serve before the kernel starts barfing, and that cap is substantially lower than the number of multiplexed streams you can push over a single TCP connection.

You’re also completely ignoring TCP slow start process, which you can bet your bottom dollar will prevent six TCP streams beating six multiplexed streams over a single TCP stream when measuring latency from first connection.